Active material excelling in high-voltage characteristics

ABSTRACT

An active material expressed by a general formula; Li a Ni b Co c Mn d D e O f  (where 0.2≤“a”≤1, “b”+“c”+“d”+“e”=1, 0≤“e”&lt;1, “D” is at least one element selected from the group consisting of Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K and Al, and 1.7≤“f”≤2.1) includes a high manganese portion, which is made of a metallic oxide including Ni, Co and Mn at least and of which the composition ratio between Ni, Co and Mn is expressed by Ni:Co:Mn=b2:c2:d2 (note that “b2”+“c2”+“d2”=1, 0&lt;“b2”&lt;1, 0&lt;“c2”&lt;“c”, and “d”&lt;“d2”&lt;1), in a superficial layer thereof.

This is a divisional of U.S. application Ser. No. 14/762,299, filed Jul.21, 2015, which is a National Stage of International Application No.PCT/JP2014 /000361 filed Jan. 24, 2014, claiming priority based onJapanese Patent Application No. 2013-011626 filed Jan. 25, 2013,Japanese Patent Application No. 2013-022849 filed Feb. 8, 2013, JapanesePatent Application No. 2013-034835 filed Feb. 25, 2013, and JapanesePatent Application No. 2013-240796 filed Nov. 21, 2013, the contents ofall of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The _(p)resent invention relates to a lithium composite metallic oxidehaving a lamellar rock-salt structure, and expressed by a generalformula, Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f) (where 0.2≤“a”≤1,“b”+“c”+“d”+“e”=1, 0≤“e”<1, “D” is at least one element selected fromthe group consisting of Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K andAl, and 1.7≤“f”≤2.1).

BACKGROUND ART

Various materials have been known to be used for active materials innonaqueous-system secondary batteries. Among the materials, lithiumcomposite metallic oxides, which have a lamellar rock-salt structure andare expressed by a general formula, Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f)(where 0.2≤“a”≤1, “b”+“c”+“d”+“e”=1, 0≤“e”<1, “D” is at least oneelement selected from the group consisting of Li, Fe, Cr, Cu, Zn, Ca,Mg, Zr, S, Si, Na, K and Al, and 1.7≤“f”≤2.1), have been useduniversally as active materials for lithium-ion secondary batteries.

However, when a lithium composite metallic oxide expressed by theaforementioned general formula is used as an active material in ahigh-capacity secondary battery driven or operated with a high voltagerequired for on-vehicle secondary battery, for instance, the lithiumcomposite metallic oxide has been unable to keep the standard forsatisfying a capacity maintained rate of the secondary battery, becausethe resistance of the material to the high voltage has beeninsufficient.

Consequently, investigations have been actively carried out recently toupgrade various materials to be used as active materials in theresistance to high voltage. In making the investigations, the followingthree methods have been proposed commonly.

1) doping an active material with an element of different species 2)forming a protective film on the surface of an active material

3) changing the composition of an active material in the superficiallayer

The method according to above-mentioned 1), and an advantageous effectthereof are concretely explained below. Doping an active material withan element, such as Al or Zr, which has not been present in the activematerial, enables degradations of the active material accompanied bycharging and discharging operations, namely, accompanied by theabsorption and release of Li, to be inhibitable.

The method according to above-mentioned 2), and an advantageous effectthereof are concretely explained below. As following Patent ApplicationPublication No. 1 discloses, making a protective film on the surface ofan active material with a salt of phosphoric acid, and preventing theactive material from contacting directly with an electrolytic solutionenable degradations of the active material resulting primarily fromcontacting with the electrolytic solution to be inhibitable.

The method according to above-mentioned 3), and an advantageous effectthereof are concretely explained below. Following Patent ApplicationPublication No. 2 discloses an active material with an increased Alcomposition in an obtainable superficial layer thereof by coating theactive material on the surface with an Al compound and then heattreating the active material with the Al compound coated thereon.

Moreover, disclosures on crystalline heterogeneous strains in lithiumcomposite metallic oxides are available in Patent ApplicationPublication Nos. 3 through 6 mentioned below.

Patent Application Publication No. 3 sets forth controlling crystallineheterogeneous strains in a lithium composite metallic oxide during a4-V-class charging/discharging cycle. The publication points out that,when crystalline heterogeneous strains in a lithium composite metallicoxide are low, namely, when the crystallinity is high, slight collapsesin the crystal structure results in greatly hindering the diffusion oflithium ions at the time of battery reactions and thereby a capacitymaintained rate becomes low. Accordingly, upgrading the capacitymaintained rate at the time of a 4-V-class charging/discharging mode oroperation has been sought for. Moreover, in Patent PublicationLiterature No. 3, crystalline heterogeneous strains in a lithiumcomposite metallic oxide are controlled by adding an element ofdifferent species to the fundamental constituent elements of the lithiumcomposite metallic oxide. Accordingly, the lithium composite metallicoxide has been feared of being declined in the capacity to such anextent that the different-species element is added. From a viewpoint ofthe capacity, not adding the different-species element to the lithiumcomposite metallic oxide is more preferable.

Patent Application Publication No. 4 sets forth that, in a hexagonalrock-salt-type crystal structure, such strains occur as stretching inthe c-axis direction because repulsion forces occur between the oxygenatoms. The publication points out that not only the strains have aninfluence on the diffusion distance of Li and the stabilization ofcrystal structure, but also the strains result in making a high-capacitypositive-electrode active material excelling in the cyclic durabilityobtainable.

Patent Application Publication No. 5 sets forth that defects and strainsin the crystal lattice of an active material relieve expansive orcontractive stresses in the lattice accompanied by charging/dischargingmode or operations and the relieved stresses result in improving theactive material in the cyclic longevity.

Patent Application Publication No. 6 sets forth that, even when asecondary battery is charged with a charge cut-off voltage of from 4.2 Vup to 4.5 V against the lithium potential, setting a c-axis variationrate of the positive-electrode active material at a predetermined valueor less leads to making the secondary battery upgradeable considerablyin the cyclability.

PATENT LITERATURE

Patent Application Publication No. 1: Japanese Unexamined PatentPublication (KOKAI) Gazette No. 2006-127932;

Patent Application Publication No. 2: Japanese Unexamined PatentPublication (KOKAI) Gazette No. 2001-196063;

Patent Application Publication No. 3: Japanese Unexamined PatentPublication (KOKAI) Gazette No. 10-079251;

Patent Application Publication No. 4: Japanese Unexamined PatentPublication (KOKAI) Gazette No. 2011-028999;

Patent Application Publication No. 5: Japanese Unexamined PatentPublication (KOKAI) Gazette No. 2004-087487; and

Patent Application Publication No. 6: Japanese Unexamined PatentPublication (KOKAI) Gazette No. 2004-356034

SUMMARY OF THE INVENTION Technical Problem

Since the three methods according to aforementioned 1) through 3) havedrawbacks given below, respectively, the methods have not necessarilyarrived at obtaining a satisfiable active material yet.

The following are the drawbacks of the method according toaforementioned 1): Since absorbable and releasable Li in the activematerial has been decreased, in effect, by doping the active materialwith the different-species element not being driven or operatedelectrochemically, the Li storage capacity in the active materialdecreases and thereby the capacity of a lithium-ion secondary battery,per se, declines.

A drawback of the method according to aforementioned 2) is that theprotective film formed on the active-material surface turns into anelectric resistance to make currents less likely to flow. Althoughmaking the protective film into an extremely-thin film is good toovercome the drawback, establishing such a technology is very difficultat the level of industrialization.

The method according to aforementioned 3) is desirable theoretically,because the method does not likely to cause a capacity to decline, thedrawback of the method according to aforementioned 1), and because anyelectrically-resistive protective film, the drawback of the methodaccording to aforementioned 2), is not formed at all. However, accordingto the disclosures of Patent Application Publication No. 2, since themethod according to aforementioned 3) is virtually a technology ofdoping the active-material superficial layer with Al, not only the samedrawbacks as 1) are observed, but also no marked advantageous effect isobserved when comparing the active material of which the Al compositionin the active-material superficial layer is increased by the treatmentmethod set forth in the publication with another active material towhich the treatment is not carried out at all.

That is, in the technologies of modifying the active materials, anactive material fully satisfying the standard is not necessarily said tobe obtainable.

The present invention is made in view of such circumstances. An objectof the present invention is to provide a lithium composite metallicoxide usable as an active material for lithium-ion secondary battery,the active material keeping a satisfactory Li storage capacity, namely,exhibiting a satisfactory capacity maintained rate, even when beingemployed for secondary batteries driven or operated with a high voltage.

Solution to Problem

As a result of earnest investigations by the present inventors, thepresent inventors came to know that, when carrying out a specifictreatment (hereinafter, being sometimes referred to as a “specifictreatment,” or a “treatment according to the present invention”) tomaterials having a lamellar rock-salt structure and expressed by ageneral formula, Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f) (where 0.2≤“a”≤1,“b”+“c”+“d”+“e”=1, 0 “e”<1, “D” is at least one element selected fromthe group consisting of Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K andAl, and 1.7≤“f”≤2.1), post-treatment lithium composite metallic oxideshad an increased Mn composition ratio in the outermost superficiallayer, regardless of the fact that Mn had not been added by thetreatment. Moreover, the present inventors came to know that thepost-treatment lithium composite metallic oxides had a changed crystalstructure in the superficial layer. In addition, the present inventorscame to know that the post-treatment lithium composite metallic oxideshad changed heterogeneous strains in the lamellar rock-salt crystalstructure. An Mn composition ratio in the outermost superficial layerincreased by the aforementioned specific treatment, a crystal structurein the superficial layer changed by the specific treatment, andheterogeneous strains in the lamellar rock-salt crystal structurechanged by the specific treatment are defined as “states changed bysurface modification” in the present specification. Moreover, thechanges are called as “surface modifications” generically.

And, the present inventors discovered that, when a lithium compositemetallic oxide after the treatment according to the present invention(hereinafter, being sometimes referred to as an “active materialaccording to the present invention,” or a “lithium composite metallicoxide according to the present invention”) is used as an active materialfor lithium-ion secondary battery, the secondary battery has a suitablymaintained capacity. In particular, the present inventors discoveredthat, even when the secondary battery is driven or operated with a highvoltage at around 4.5 V, the secondary battery exhibits an excellentcapacity maintained rate.

That is, an active material according to the present invention has alamellar rock-salt structure, and is expressed by a general formula,Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f) (where 0.2≤“a”≤1, “b”+“c”+“d”+“e”=1,0≤“e”<1, “D” is at least one element selected from the group consistingof Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K and Al, and1.7≤“f”≤2.1); and the present active material comprises a high manganeseportion, which is made of a metallic oxide including Ni, Co and Mn atleast and of which the composition ratio between Ni, Co and Mn isexpressed by Ni:Co:Mn=b2:c2:d2 (note that “b2”+“c2”+“d2”=1, 0<“b2”<1,0<“c2”<“c”, and “d”<“d2”<1), in a superficial layer thereof.

A lithium-ion secondary battery using the present active materialexhibits an excellent capacity maintained rate, because the followingreasons are inferred from a viewpoint of the composition in thesuperficial layer.

When an active material, which belongs to a lamellar rock-salt type andis expressed by the general formula: Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f)(where 0.2≤“a”≤1, “b”+“c”+“d”+“e”=1, 0≤“e”<1, “D” is at least oneelement selected from the group consisting of Li, Fe, Cr, Cu, Zn, Ca,Mg, Zr, S, Si, Na, K and Al, and 1.7≤“f”≤2.1), is used for a lithium-ionsecondary battery, the transition metals, Ni, Co and Mn, in the generalformula are believed to have the following roles.

Ni is the most active at the time of Li charging/discharging reactions.Although the greater the Ni content is within an active material themore the capacity increases, the greater the Ni content is within anactive material the more the active material is likely to degradecontrarily.

Mn is the most inactive at the time of Li charging/dischargingreactions. Although the greater the Mn content is within an activematerial the more the capacity declines, the greater the Mn content iswithin an active material the more the active material excels in thestability of the crystal structure contrarily.

Co exhibits an intermediate activity between the activities of Ni and Mnat the time of Li charging/discharging reactions. The Co content withinan active material also affects the capacity and stability to anintermediate extent between Ni and Mn.

If so, when the Mn composition ratio in the active-material superficiallayer becomes high compared with an Mn composition ratio inside theactive material, the stability of the active-material superficial layer,which undergoes the inflow and outflow of Li actively and contacts withan electrolyte directly, comes to upgrade relatively. As a result, theactive material comes to be inhibited from degrading. Note herein that,since the composition change in the active-material superficial layer isslight extremely when viewing the active material as a whole, minimizingthe activity decline, which results from heightening the Mn compositionratio in the active-material superficial layer, is made possible at thetime of Li charging/discharging reactions.

Moreover, another active material according to the present invention isan active material having a lamellar rock-salt structure and expressedby a general formula, Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f) (where0.2≤“a”≤1, “b”+“c”+“d”+“e”=1, 0≤“e”<1, “D” is at least one elementselected from the group consisting of Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S,Si, Na, K and Al, and 1.7≤“f”≤2.1) ; and

the active material comprises a first superlattice-structure portion inan active-material superficial layer thereof, the firstsuperlattice-structure portion exhibiting a seven-set averaged value “n”of intensity ratios being less than 0.9 when the intensity ratios arecomputed in seven sets by dividing a minimum value of three continuousintegrated intensities of an image, which is obtained by observingidentical 3 b sites in said lamellar rock-salt structure from a <1-100>orientation with a high-angle scattering annular dark-field scanningtransmission electron microscope, by a maximum value of the threecontinuous integrated intensities.

In addition, still another active material according to the presentinvention is an active material having a lamellar rock-salt structure,and expressed by general formula, Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f)(where 0.2≤“a”≤1, “b”+“c?+“d”+“e”=1, 0≤“e”<1, “D” is at least oneelement selected from the group consisting of Li, Fe, Cr, Cu, Zn, Ca,Mg, Zr, S, Si, Na, K and Al, and 1.7≤“f”≤2.1); and the active materialcomprises a second superlattice-structure portion in an active-materialsuperficial layer thereof, wherein three arbitrary continuous integratedstrengths of an image, which is obtained by observing identical 3 bsites in said lamellar rock-salt structure from a <1-100> orientationwith a high-angle scattering annular dark-field scanning transmissionelectron microscope, are expressed in the following order: p1, p2, and q(where 0.9×“p1”≤“p2”≤1.1×“p1”, “q” is “q”<0.9×“p2” when “p1”≤“p2”, or“q” is “q”<0.9×“p1” when “p2”≤“p1”).

Additionally, a further active material according to the presentinvention is an active material having a lamellar rock-salt structure,and expressed by a general formula, Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f)(where 0.2≤“a”≤1, “b”+“c”+“d”+“e”=1, 0≤“e”<1, “D” is at least oneelement selected from the group consisting of Li, Fe, Cr, Cu, Zn, Ca,Mg, Zr, S, Si, Na, K and Al, and 1.7≤“f”≤2.1); and

the active material comprises a third superlattice-structure portion inan active-material superficial layer thereof, the thirdsuperlattice-structure portion satisfying both of the conditions for thefirst superlattice-structure portion as set forth above and theconditions for the second superlattice-structure portion as set forthabove.

Note herein that, compared with the interior of the active material, theaforementioned first superlattice-structure portion, secondsuperlattice-structure portion and third superlattice-structure portion,which exist in the active-material superficial layer, excel in theresistance property against the degradations accompanied bycharging/discharging modes or operations. To be concrete, theaforementioned first through third superlattice-structure portions excelin the structural stability when Li is pulled from out of the presentlithium composite metallic oxide at the time of charging a lithium-ionsecondary battery, and excel in the corrosion resistance againstelectrolytes for lithium-ion secondary battery. Thus, the stability ofthe active-material superficial layer, which undergoes the inflow andoutflow of Li actively and contacts with an electrolyte directly, comesto upgrade relatively. As a result, the present active material comes tobe inhibited from degrading.

And, a lithium composite metallic oxide according to the presentinvention is a lithium composite metallic oxide having a lamellarrock-salt crystal structure, and expressed by a general formula:Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f) (where 0.2≤a”≤1, “b”+“c”+“d”+“e”=1,0≤“e”<1, is at least one element selected from the group consisting ofLi, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K and Al, and 1.7≤“f”≤2.1);and

said lamellar rock-salt crystal structure comprises a heterogeneousstrain in a c- axis direction of said lamellar rock-salt crystalstructure.

In the light of the aforementioned disclosures of Patent ApplicationPublication Nos. 3 through 6, a secondary battery, which uses as apositive-electrode active material the present lithium compositemetallic oxide comprising a heterogeneous strain in a c-axis directionof the lamellar rock-salt crystal structure, is expectable to haveexcellent cyclability.

Advantageous Effects of the Invention

The present lithium composite metallic oxide keeps a satisfactory Listorage capacity, namely, exhibits a satisfactory capacity maintainedrate, even when being employed for a secondary battery driven oroperated with a high voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an ordinary superlattice plane ofNi_(1/3)Co_(1/3)Mn_(1/3) in which a plane constituted of alamellar-rock-salt-structure 3 b site is represented as a [√3×√3]R30°type;

FIG. 2 is an image corresponding to a lamellar-rock-salt-structure 3b-site plane which is constituted of the present first through thirdsuperlattice-structure portions observed by a high-angle scatteringannular dark-field scanning transmission electron microscopy;

FIG. 3 is an image of a lamellar-rock-salt-structure 3 b-site planecomprising an ordinary superlattice plane which is observed by ahigh-angle scattering annular dark-field scanning transmission electronmicroscopy, wherein commercially available lamellar rock-salt-typeLiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ was measured;

FIG. 4 is an image in the vicinity of a boundary between an ordinarysuperlattice plane and the present first through thirdsuperlattice-structure portions which were observed by a high-anglescattering annular dark-field scanning transmission electron microscopy;

FIG. 5 is data on integrated intensities of the image shown in FIG. 4;

FIG. 6 is a schematic diagram of a lamellar rock-salt structure in alithium composite metallic oxide according to the present invention;

FIG. 7 is an X-ray diffraction pattern of an active material accordingto a twelfth example, and an X-ray diffraction pattern of an untreatedproduct according to a third comparative example; and

FIG. 8 is an SEM-EDX chart of the active material according to thetwelfth example, and an SEM-EDX chart of the untreated product accordingto the third comparative example.

DESCRIPTION OF THE EMBODIMENTS

Some of best modes for executing the present invention are hereinafterdescribed. Note that, unless otherwise specified, numerical ranges,namely, “from ‘x’ to ‘y’” set forth in the present description, involvethe lower limit, “x,” and the upper limit, “y” in the ranges. Moreover,the other numerical ranges are composable by arbitrarily combining anytwo of the upper-limit values and lower-limit values, involving theother numeric values enumerated in examples as well. In addition,selecting numeric values arbitrarily from within the ranges of numericvalues enables other upper-limit and lower-limit numerical values to beset.

An active material according to the present invention has a lamellarrock-salt structure, and is expressed by a general formula,Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f) (where 0.2≤“a”≤1, “b”+“c”+“d”+“e”=1,0≤“e”<1, “D” is at least one element selected from the group consistingof Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K and Al, and1.7≤“f”≤2.1), and the present active material comprises a high manganeseportion, which is made of a metallic oxide including Ni, Co and Mn atleast and of which the composition ratio between Ni, Co and Mn isexpressed by Ni:Co:Mn=b2:c2:d2 (note that “b2”+“c2”+“d2”=1, 0<“b2”<1,0<“c2”<“c”, and “d”<“d2”<1), in the superficial layer.

In the general formula: Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f) (where0.2≤“a”≤1, “b”+“c”+“d”+“e”=1, 0≤“e”<1, “D” is at least one elementselected from the group consisting of Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S,Si, Na, K and Al, and 1.7≤“f”=2.1), the values of “b,” “c” and “d” arenot at all restricted especially, as far as the values satisfy theaforementioned conditions. However, allowable values of “b”, “c” and “d”fall in such ranges as 0≤“b”≤1, 0≤“c”≤1 and 0≤“d”≤1, respectively; and amore allowable values thereof fall in such ranges as 0<“b”<1, 0<“c”<1and 0<“d”<1, respectively. Moreover, at least one of “b,” “c” and “d”falls preferably in such a range as 0<“b”<80/100, 0<“c”<70/100 and10/100<“d”<1, respectively; more preferably in such a range as10/100<“b”<68/100, 12/100<“c”<60/100 and 20/100≤“d”<68/100,respectively; and much more preferably falls in such a range as25/100<“b”<60/100, 15/100<“c”<50/100 and 25/100<“d”<60/100,respectively. In addition, especially preferable ranges are1/3≤“b”≤50/100, 20/100≤“c”≤1/3 and 30/100≤“d”≤1/3, respectively.Moreover, the most preferable values of “b,” “c” and “d” are as follows:“b”=1/3, “c”=1/3 and “d”=1/3; or “b”=50/100, “c”=20/100 and “d”=30/100.

Permissible values of “a,” “e” and “f” are numerical values fallingwithin the ranges prescribed by the general formula, and areexemplifiable as follows: “a”=1, “e”=0 and “f”=2.

The high manganese portion is hereinafter explained.

The high manganese portion is a metallic oxide, which includes Ni, Coand Mn at least, and of which the composition ratio between Ni, Co andMn is expressed by Ni:Co:Mn=b2:c2:d2 (note that “b2”+“c2”+“d2”=1,0<“b2”<1, 0<“c2”<“c”, and “d”<“d2”<1).

The values of aforementioned “b2,” “c2” and “d2” are not restricted atall, as far as the values satisfy the aforementioned conditions.

A preferable value of “b2” falls in such a range as 0<“b2”<80/100; amore preferable value thereof falls in such a range as20/100<“b2”<70/100; and a much more preferable value thereof falls insuch a range as 25/100<“b2”<50/100. Alternatively, a preferable value of“b2” falls in such a range as 0.5×“b”<“b2”<2×“b”; a more preferablevalue thereof falls in such a range as 0.8×“b”<“b2”<1.4×“b”; and a muchmore preferable value thereof falls in such a range as0.85×“b”<“b2”<1.1×“b”. An especially preferable value of “b2” falls insuch a range as 0.88×“b”<“b2”≤0.96×“b”.

A more preferable value of “c2” falls in such a range as 5/100<“c2”<“c”;and a much more preferable value thereof falls in such a range as10/100<“c2”<25/100. Alternatively, a preferable value of “c2” falls insuch a range as 0.2×“c”<“c2”<0.9×“c”; a more preferable value thereoffalls in such a range as 0.5×“c”<“c2”<0.88×“c”; a much more preferablevalue thereof falls in such a range as 0.63×“c”≤“c2”≤0.85×“c”.

A more preferable value of “d2” falls in such a range as35/100<“d2”<85/100; and a much more preferable value thereof falls insuch a range as 36/100<“d2”<65/100. Moreover, another preferable valueof “d2” falls in such a range as “d”<“d2”<85/100; another morepreferable value thereof falls in such a range as “d”<“d2”<75/100; andanother much more preferable value thereof falls in such a range as“d”<“d2”<65/100. In addition, still another preferable value of “d2”falls in such a range as “d”<“d2”<2×“d”; still another more preferablevalue thereof falls in such a range as 1.1×“d”<“d2”<1.5×“d”; and stillanother much more preferable value thereof falls in such a range as1.2×“d”<“d2”≤1.41×“d”.

The phrase, “comprising a high manganese portion in the superficiallayer,” means that the high manganese portion exists in the superficiallayer, regardless of the amount being more or less. As far as the highmanganese portion exists in the superficial layer of an active material,the stability is kept for the active material, which is present moreinside at least than is a location where the high manganese portionexists. As a result, the advantageous effect of maintaining the capacityis demonstrated. In view of maintaining the capacity, a preferable highmanganese portion exists in the entire superficial layer of an activematerial.

The term, “superficial layer,” means a layer including the outermostsurface of the present active material. From the viewpoint of thestability of the present active material, a thickness of the superficiallayer is said that the thicker the thickness is the more preferably thesuperficial layer is made. However, no practical problem arises, as faras the superficial layer has an enough thickness for preventing thecontact between an electrolytic solution and the interior of an activematerial. Considering the likeliness of the progress of Licharging/discharging reactions, the thinner a thickness of thesuperficial layer is the more preferably the superficial layer is made.A thickness “t” (nm) of the superficial layer falls in such a range as0<“t”<20, for instance. A preferable thickness “t” falls in such a rangeas 0.01<“t”<10; a more preferable thickness “t” falls in such a range as0.1<“t”<5; a much more preferable thickness “t” falls in such a range as1<“t”<3; and the most preferable thickness “t” falls in such a range as1.5<“t”<2.5.

The high manganese portion is also allowed to scatter in the superficiallayer, or is even permitted to exist as a layer of the high manganeseportion. A thickness “s₁” (nm) of a layer of the high manganese portionfalls in such a range as 0<“s₁”<20, for instance. A preferable thickness“s₁” falls in such a range as 0.01<“s₁”<10; a more preferable thickness“s₁” falls in such a range as 0.1<“s₁”<5; a much more preferable “s₁”falls in such a range as 1<“s₁”<3; and the most preferable thickness“s₁” falls in such a range as 1.5<“s₁”<2.5.

Moreover, a preferable high manganese portion exists within a range of 2nm at least from the surface of an active material in a direction towardthe center of the active material.

The high manganese portion exists in the superficial layer of thepresent active material. And, since the superficial layer accounts for aslight volume compared with the volume of the present active material,the composition of the high manganese portion does not have anyinfluence virtually on the composition of an active material with thegeneral formula: Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f) (where 0.2≤“a”≤1,“b”+“c”+“d”+“e”=1, 0≤“e”<1, “D” is at least one element selected fromthe group consisting of Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K andAl, and 1.7≤“f”≤2.1).

Next, the lamellar rock-salt structure is hereinafter explained.

The crystal structure of a lithium composite metallic oxide expressed bythe general formula: Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f) (where0.2≤“a”≤1, “b”+“c”+“d” +“e”=1, 0≤“e”<1, “D” is at least one elementselected from the group consisting of Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S,Si, Na, K and Al, and 1.7≤“f”≤2.1), belongs to a rhombohedral system,has a threefold axis (which exhibits an inversion symmetry) andmirror-symmetry plane, and is expressed by the space group “R-3m”. Notethat, in the designation, “R-3m”, “-3” expresses the number 3 to whichan overline added. And, the lamellar rock-salt structure of a lithiumcomposite metallic oxide with the aforementioned general formulacomprises the 3a sites of a layer (or plane) including Li_(a), the 3 bsites of another layer (or plane) including Ni_(b)Co_(c)Mn_(d)D_(e), andthe 6 c sites of still another layer (or plane) including O_(f), whereinthe sites are repeated in the order of the 6 c site, the 3 b site, the 6c site, the 3 a site, and so on. Note herein that the “3 a site,” the “3b site” and the “6 c” site are designations expressed in accordance withthe Wyckoff symbols.

The first through third superlattice-structure portions are hereinafterexplained.

The term, a “first superlattice-structure portion,” means a structureexhibiting a seven-set averaged value “n” of intensity ratios being lessthan 0.9 when the intensity ratios are computed in seven sets bydividing a minimum value of three continuous integrated intensities ofan image, which is obtained by observing identical 3 b sites in saidlamellar rock-salt structure from a <1-100> orientation with ahigh-angle scattering annular dark-field scanning transmission electronmicroscope, by a maximum value of the three continuous integratedintensities. Note that, in the designation, “<1-100>”, “-1” expressesthe number 1 to which an overline added. The term, a “<1-100>orientation,” is one of generalized expressions for the equivalentvectors of vectors expressing directions within a crystal by the Millerindices. Note herein that, in a crystal plane of the 3 b site shown inFIG. 1, an orientation, which is inclined to the right by 30° from aline connecting nickel, cobalt and manganese in this order in adirection from the bottom toward the top, is given concretely as one ofthe <1-100> orientations in the 3 b-site plane of a lamellar rock-saltstructure. The aforementioned averaged value “n” is not at allrestricted especially, as far as the value is less than 0.9. However, apreferable averaged value “n” is less than 0.86, a more preferableaveraged value “n” is less than 0.82, and a much more preferableaveraged value “n” is less than 0.80.

The term, a “second superlattice-structure portion,” means a structurein which three arbitrary continuous integrated strengths of an image,which is obtained by observing identical 3 b sites in said lamellarrock-salt structure from a <1-100> orientation with a high-anglescattering annular dark-field scanning transmission electron microscope,are expressed in the following order: p1, p2, and q (where0.9×“p1”≤“p2”≤1.1×“p1”, “q” is “q”<0.9×“p2” when “p1”≤“p2”, or “q” is“q”<0.9×“p1” when “p2”≤“p1”). The values of aforementioned “p1, ” “p2 ”and “q” are not at all restricted especially, as far as the values fallin the above-described ranges, respectively. However, when “p1”≤“p2”, apreferable value of “q” is “q”<0.85×“p2”; a more preferable valuethereof is “q”<0.80×“p2”; and a much more preferable value thereof is“q”<0.75×“p2”. Likewise, when “p2”≤“p1”, a preferable value of “q” is“q”<0.85×“p1”; a more preferable value thereof is “q”<0.80×“p1”; and amuch more preferable value thereof is “q”<0.75×“p1”.

Journal of The Electrochemical Society, 151 (10), pp. A1545-A1551 (2004)discloses a superlattice plane in the Ni_(1/3)Co_(1/3)Mn_(1/3) crystalplanes constituted of the 3 b sites of a lamellar rock-salt structure inLiNi_(1/3)Co_(1/3)Mn_(1/3)O₂. According to the Wood's designation, theaforementioned Ni_(1/3)Co_(1/3)Mn_(1/3) superlattice plane isrepresentable as a [√3×X √3]R30° type. FIG. 1 shows a schematic diagramof the Ni_(1/3)Co_(1/3)Mn_(1/3) superlattice plane represented by a[√3×√3]R30° type.

Note that, in the subsequent descriptions, a superlattice plane, whichis able to exist before a treatment according to the present invention,is referred to as an “ordinary superlattice plane.”

The “high-angle scattering annular dark-field scanning transmissionelectron microscopy” is the so-called HAADF-STEM, and is referred to asa method in which a finely-tuned electron beam is projected onto asample while scanning the sample, some of the transmission electronsscattering at high angles are detected with an annular detector, andintegrated strengths of the detected electrons are displayed.

In the present invention, the crystal plane of an active materialmeasured by the high-angle scattering annular dark-field scanningtransmission electron microscopy is a metallic layer including Ni, Coand Mn, and is a plane corresponding to the superlattice plane accordingto the aforementioned literature.

When observing the [√3×√3]R30°-type Ni_(1/3)CO_(1/3)Mn_(1/3) ordinarysuperlattice plane in LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ from a <1-100>orientation by the high-angle scattering annular dark-field scanningtransmission electron microscopy and then computing strength ratios inseven sets by dividing a minimum value of three continuous integratedstrengths obtained from an identical 3 b-site in a lamellar rock-saltstructure in an image, which is observed with a high-angle scatteringannular dark-field scanning transmission electron microscope, by amaximum value of the three continuous integrated strengths, an averagedvale “n” of the seven sets is 0.9 or more and less than one. Moreover,when observing the same ordinary superlattice plane from a <1-100>orientation by the high-angle scattering annular dark-field scanningtransmission electron microscopy, three arbitrary continuous integratedstrengths, which are obtained from an identical 3b-site in the lamellarrock-salt structure in an image observed with a high-angle scatteringannular dark-field scanning transmission electron microscope, arearranged in the following order: p1, p2 and p3 (where0.9×“p1”≤“p2”≤1.1×“p1”, 0.9×“p1”≤“p3”≤1.1×“p1”, 0.9×“p2”≤“p3”≤1.1×“p2”).That is, in the [√3×√3]R30°-type Ni_(1/3)Co_(1/3)Mn_(1/3) ordinarysuperlattice plane in LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂, no marked differencewas appreciated in the integrated strengths observed in an identical 3b-site plane in the lamellar rock-salt structure. Hence, theaforementioned ordinary superlattice layer, and the first through thirdsuperlattice-structure portions according to the present invention aredistinguished one another definitely. In the first through thirdsuperlattice-structure portions of the present active material, of thethree continuous integrated strengths, the latter one strength is smallcompared with the two former strengths. In other words, the firstthrough third superlattice-structure portions of the present activematerial are also said to exhibit an integrated-strength pattern inwhich the integrated-strength pattern obtained from the ordinarysuperlattice plane expressed as (√3×√3]R30° type is disorderedregularly.

The phrase, “comprising a first, second or third superlattice-structureportion in the active-material superficial layer,” means that the first,second or third superlattice-structure portion exists, regardless of theamount being more or less. As far as the first, second or thirdsuperlattice-structure portion exists in the superficial layer of anactive material, the stability is kept for the active material, which ispresent more inside at least than is a location where the first, secondor third superlattice-structure portion exists. As a result, theadvantageous effect of maintaining the capacity is demonstrated. In viewof maintaining the capacity, a preferable first, second or thirdsuperlattice-structure portion exists in the entire superficial layer ofan active material.

The term, “superficial layer,” means a layer including a surface of thepresent active material. From the viewpoint of the stability of the present active material, a thickness of the superficial layer is said thatthe thicker the thickness is the more preferably the superficial layeris made. However, no practical problem arises, as far as the superficiallayer has an enough thickness for preventing the contact between anelectrolytic solution and the interior of an active material.Considering the likeliness of the progress of Li charging/dischargingreactions, the thinner a thickness of the superficial layer is the morepreferably the superficial layer is made. A thickness “t” (nm) of thesuperficial layer falls in such a range as 0.1<“t”<20, for instance. Apreferable thickness “t” falls in such a range as 0.01<“t”<10; a morepreferable thickness “t” falls in such a range as 0.1<“t”<5; a much morepreferable thickness “t” falls in such a range as 1<“t”<3; and the mostpreferable thickness “t” falls in such a range as 1.5<“t”<2.5.

The first, second or third superlattice-structure portion is alsoallowed to scatter in the superficial layer, or is even permitted toexist as a layer of the first, second or third superlattice-structureportion. A thickness “s₂” (nm) of the layer of the first, second orthird superlattice-structure portion falls in such a range as 0<“s₂”<20,for instance. A preferable thickness “s₂” falls in such a range as0.01<“s₂”<10; a more preferable thickness “s₂” falls in such a range as0.1<“s₂”<5; a much more preferable thickness “s₂” falls in such a rangeas 1<“s₂”<3; and the most preferable thickness “s₂” falls in such arange as 1.5<“s₂”<2.5.

The interior of the present active material is not restricted at all, asfar as the interior is expressed by a general formula:Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f) (where 0.2≤“a”≤1, “b”+“c”+“d”+“e”=1,0≤“e”<1, “D” is at least one element selected from the group consistingof Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K and Al, and1.7≤“f”≤2.1). A preferable interior thereof comprises a [√3×√3]R30° typeordinary superlattice plane.

Moreover, FIG. 6 schematically shows the lamellar rock-salt crystalstructure of a lithium composite metallic oxide. As shown in FIG. 6, inthe lamellar rock-salt crystal structure, an Li group 1, an O group 2,an (Ni, Mn, Co) group 3, and an O group 4 are formed lamellarly on thea-b plane formed between the a-axis and b-axis, respectively. In thec-axis direction, the Li group 1, the O group 2, the (Ni, Mn, Co) group3, and the O group 4 are repeated in this order.

The lamellar rock-salt crystal structure of the present lithiumcomposite metallic oxide comprises a heterogeneous strain η_(c) in thecrystalline c-axis direction, and a heterogeneous strain η in theall-round direction. The heterogeneous strains are believed to beattributed to grain boundaries in the present lithium composite metallicoxide, defects like dislocations therein, or mismatches between thephase interfaces therein. Causing such uneven regions to occur withinthe crystals in a lithium composite metallic oxide leads to stabilizingthe crystal structure. Accordingly, a secondary battery using thepresent lithium composite metallic oxide as a positive-electrode activematerial is believed to be able to enhance the capacity maintained rate,and to enhance the charging/discharging cyclability.

The c-axis-direction heterogeneous strain η_(c), and theall-round-direction heterogeneous strain η are computable from X-raydiffraction lines obtainable by analyzing a lithium composite metallicoxide with an X-ray diffraction apparatus. According to theStokes-Wilson's law, there is a relationship defined by followingEquation (1) between a heterogeneous strain η in the crystal lattice ofa lithium composite metallic oxide and an integrated width β_(j) in thepeak of X-ray diffraction lines resulting from the heterogeneous strainη.

β_(j)=2η tan θ  (1) (Here, θ is a Bragg angle.)

Moreover, according to the Scherrer's law, there is another relationshipdefined by following equation (2) between a size D of the crystallattice and another integrated width β_(i) in the peak of X-raydiffraction lines resulting from the size D.

D=λ/(β_(i) cos θ)   (2) (Here, λ is the wavelength of an X-ray formeasurement.)

In addition, according to the Hall's law, still another integrated widthβ resulting from both of the crystal-lattice size D and crystal-latticeheterogeneous strain η has a still another relationship defined byfollowing Equation (3).

β=β_(i)+β_(j)   (3)

Following relational Equation (4) is derivable eventually fromabove-mentioned Equations (1) through (3).

(β cas θ)/λ=1/D+2η(sin θ)/λ  (4)

The heterogeneous strain η is found from the gradient of a line, whichis made obtainable by measuring the integrated width β of each of thepeaks of the respective diffraction lines, substituting the measuredvalues into Equation (4), and then plotting the values of (β cos θ)/λagainst (sin θ)/λ. Note that the β, each of the integrated widths, wascomputed by an equation, (Integrated Area in Peak of Diffract ionLine)/(Peak Height of Diffraction Line). Note that, when finding thec-axis-direction heterogeneous strain η_(c), the heterogeneous strainη_(c) is findable by plotting the values of (β cos θ)/λ of peaks, whichresult from the (006), (009) and (0012) crystal planes, against (sinθ)/λ.

In the present lithium composite metallic oxide with a lamellarrock-salt crystal structure, a preferable c-axis-direction heterogeneousstrain η_(c) is from 0.04 or more to 0.10 or less; and a more preferablec-axis-direction heterogeneous strain η_(c) is from 0.05 or more to 0.10or less. Moreover, a desirable c- axis-direction heterogeneous strainη_(c)is from0.055 or more to 0.095 or less. A lithium composite metallicoxide with too small a heterogeneous strain η_(c) means that thecrystallinity degree is high. And, when the crystallinity degree of alithium composite metallic oxide is high, a slight collapse in thecrystal structure results in making the diffusion of lithium ions likelyto be hindered, and thereby a fear of declining the capacity maintainedrate of a lithium-ion secondary battery arises probably. A lithiumcomposite metallic oxide with too large a heterogeneous strain η_(c)probably leads to such a fear that the crystals have collapsed easily.

In the lithium composite metallic oxide with a lamellar rock-saltcrystal structure, a preferable all-round-direction heterogeneous strainη is from 0.06 or more to 0.11 or less. A lithium composite metallicoxide with too large an all-round-direction heterogeneous strainprobably leads to such a fear that the crystals have collapsed easily.

Moreover, a suitable relationship between the c-axis-directionheterogeneous strain η_(c) and the all-round-direction heterogeneousstrain η is also showable for every transition-metal composition of thepresent lithium composite metallic oxide.

When a material, to which a treatment according to the present inventionis carried out, comprises LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂, the presentactive material exhibits preferably a value of η_(c)/η falling within arange of from 0.85 to 1.1; exhibits more preferably a value thereoffalling within a range of from 0.86 to 1.05; and exhibits much morepreferably a value thereof falling within a range of from 0.90 to 1.0.Moreover, when a material, to which a treatment according to the presentinvention is carried out, comprises LiNi_(5/10)CO_(2/10)Mn_(3/10)O₂, thepresent active material exhibits preferably a value of η_(c)/η being0.85 or less; exhibits more preferably a value thereof falling within arange of from 0.30 to 0.80; exhibits much more preferably a valuethereof falling within a range of from 0.35 to 0.75; and exhibitsespecially preferably a value thereof falling within a range of from0.40 to 0.70.

The present active material is not at all restricted especially in theconfiguration. However, mentioning the configuration in light of anaverage particle diameter of the secondary agglomerate, a preferableaverage particle diameter is 100 μm or less; and a more preferableaverage particle diameter is from 1 μm or more to 50 μm or less. Whenbeing less than 1 μm, such a drawback arises probably that theadhesiveness between an active material and a current collector islikely to be impaired, or the like, upon fabricating an electrode usingthe active material. Exceeding 100 μm probably leads to affecting thesize of an electrode, to causing such a drawback that the separatorconstituting a secondary battery has been damaged, and so on. Note thatcomputing the average particle diameter by measuring the secondaryagglomerate instrumentally with a common particle-diameter-distributionmeter is also allowed, or observing the secondary agglomerate with amicroscope to compute the average particle diameter is even permitted.

Next, a production process for the present active material ishereinafter explained. The present active material is producible bycarrying out a specific treatment (i.e., a treatment according to thepresent invention) to a material belonging to a lamellar rock-salt type,and expressed by the general formula: Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f)(where 0.2≤“a”≤1, “b”+“c”+“d”+“e”=1, 0≤“e”<1, “D” is at least oneelement selected from the group consisting of Li, Fe, Cr, Cu, Zn, Ca,Mg, Zr, S, Si, Na, K and Al, and 1.7≤“f”≤2.1).

Following a publicly-known conventional production process using ametallic oxide, a metallic hydroxide or a metallic salt like a metalliccarbonate is allowed to produce the material belonging to a lamellarrock-salt type and expressed by the general formula:Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f) (where 0.2≤“a”≤1, “b”+“c”+“d”+“e”=1,0≤“e”<1, “D” is at least one element selected from the group consistingof Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K and Al, and1.7≤“f”≤2.1), or using such a material as being available commerciallyis even permitted.

For example, when using lithium carbonate, nickel sulfate, manganesesulfate and cobalt sulfate, the material is producible as follows (i.e.,a coprecipitation method). A sulfate-salt aqueous solution includingnickel sulfate, cobalt sulfate and manganese sulfate in a predeterminedamount, respectively, is alkalified to obtain a coprecipitated slurry,and then the slurry is dried, thereby obtaining anickel/cobalt/manganese composite hydroxide. The nickel/cobalt/manganesecomposite hydroxide is dispersed in a sodium hydroxide-containing sodiumpersulfate aqueous solution, thereby synthesizing anickel/cobalt/manganese composite oxyhydroxide. A material belonging toa lamellar rock-salt type, and expressed by the general formula:Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f) (where 0.2≤“a”≤1, “b”+“c”+“d”+“e”=1,0≤“e”<1, “D” is at least one element selected from the group consistingof Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K and Al, and 1.7≤“f”≤2.1)is made obtainable by mixing a predetermined amount of lithium carbonatewith the nickel/cobalt/manganese composite oxyhydroxide and thencalcining the mixture. Giving the obtained material a desirable particlediameter is also allowed by suitably carrying out a pulverizationtreatment to the material.

Other than the above, the material belonging to a lamellar rock-salttype, and expressed by the general formula:Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f) (where 0.2≤“a”≤1, “b”+“c”+“d”+“e”=1,0≤“e”<1, “D” is at least one element selected from the group consistingof Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K and Al, and 1.7≤“f”≤2.1)is made producible by using a known method, such as a molten saltmethod, a solid phase method, a spray drying method or a hydrothermalmethod, to a mixed raw material comprising a lithium raw materialcontaining lithium, and a metallic raw material including one or moremembers selected from the group consisting of Ni, Mn and Co.

The solid phase method is a method for obtaining a lithium compositemetallic oxide by mixing or pulverizing a powder of the mixed rawmaterial, drying or powder-compact molding the powder, if needed, andthen heating or calcining the powder. A solid phase method having beencarried out usually is such that the respective raw materials are mixedone another in proportions in compliance with the composition of alithium composite metallic oxide to be produced. A preferabletemperature for heating the raw-material mixture in the solid phasemethod is from 900° C. or more to 1,000° C. or less, and a preferabletime for heating the raw-material mixture therein is from eight hours ormore to 24 hours or less.

The spray drying method is a method in which a powder of the mixed rawmaterial is dissolved in a liquid to make a solution, the solution issprayed into the air to make a mist, and then the solution having beenturned into the mist is heated. In the spray drying method, furtherheating the resultant mist is also allowed. A preferable temperature forheating the misted solution in the spray drying method is from 500° C.or more to 1,000° C. or less, and a preferable time for heating themisted solution therein is from three hours or more to eight hours orless.

The hydrothermal method is a method in which the raw materials are mixedwith water to make a mixed liquid, and the mixed liquid is heated at ahigh temperature under a high pressure. A preferable temperature forheating the mixed liquid in the hydrothermal method is from 120° C. ormore to 200° C. or less, and a preferable time for heating the mixedliquid therein is from two hours or more to 24 hours or less.

The molten salt method is a method in which a lithium compound is fusedto turn into a molten salt by heating a raw-material mixture includingthe lithium compound, and then a lithium composite metallic oxide issynthesized within a liquid of the molten salt. In the molten saltmethod, a lithium raw material not only makes a supply source of Li, butalso performs a role of adjusting the oxidizing power of the moltensalt. A preferable ratio of Li in the lithium composite metallic oxideto Li in the lithium compound (i.e., (Li in Lithium Composite MetallicOxide)/(Li in Lithium Compound)) is allowed to be less than one by molarratio.

However, the ratio is preferably from 0.02 or more to less than 0.7, ismore preferably from 0.03 to 0.5, and is much more preferably from 0.04to 0.25, by molar ratio.

Next, a treatment according to the present invention is hereinafterexplained. The present treatment is allowed to comprise any of followingTreatments 1 through 4.

(Treatment 1) comprising the steps of:

1-1) readying an acidic metallic salt aqueous solution;

1-2) mixing the metallic salt aqueous solution with a material expressedby the aforementioned general formula;

1-3) mixing a liquid obtained at said step 1-2) with anammonium-phosphate salt aqueous solution; and

1-4) isolating the present active material from another liquid obtainedat said step 1-3);

(Treatment 2) comprising the steps of:

2-1) readying an ammonium-phosphate salt aqueous solution;

2-2) mixing the ammonium-phosphate salt aqueous solution with a materialexpressed by the aforementioned general formula;

2-3) mixing a liquid obtained at said step 2-2) with an acidic metallicsalt aqueous solution; and

2-4) isolating the present active material from another liquid obtainedat said step 2-3);

(Treatment 3) comprising the steps of:

3-1) readying an aqueous solution of an ammonium-phosphate salt, or anaqueous solution of a metallic salt and an ammonium-phosphate salt;

3-2) mixing the aqueous solution with a material expressed by theaforementioned general formula; and

3-3) isolating the present active material from a liquid obtained atsaid step 3-2); or

(Treatment 4) comprising the steps of:

4-1) readying an acidic metallic salt aqueous solution, and anammonium-phosphate salt aqueous solution, respectively;

4-2) mixing water with a material expressed by the aforementionedgeneral formula;

4-3) mixing a liquid obtained at said step 4-2), said acidic metallicsalt aqueous solution, and said ammonium-phosphate salt aqueous solutionone another; and

4-4) isolating the present active material from another liquid obtainedat said step 4-3).

The respective treatments are hereinafter described more concretely.

Treatment 1: an acidic metallic salt aqueous solution is readied, andthen a material, which belongs to a lamellar rock-salt type and isexpressed by the general formula: Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f)(where 0.2≤“a”≤1, “b”+“c”+“d”+“e”=1, 0≤“e”<1, “D” is at least oneelement selected from the group consisting of Li, Fe, Cr, Cu, Zn, Ca,Mg, Zr, S, Si, Na, K and Al, and 1.7≤“f”≤2.1), is added to and stirredin the readied aqueous solution to make a mixed-and-dispersed solution.Subsequently, an ammonium-phosphate salt aqueous solution is furtheradded to and stirred in the above-mentioned mixed-and-dispersed solutionbeing put in a stirred state. The stirring operation is continued forfrom 15 minutes to one hour approximately. The present active materialis isolated by filtering.

Treatment 2: an ammonium-phosphate salt aqueous solution is readied, andthen a material, which belongs to a lamellar rock-salt type and isexpressed by the general formula: Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f)(where 0.2≤“a”≤1, “b”+“c”+“d”+“e”=1, 0≤“e”<1, “D” is at least oneelement selected from the group consisting of Li, Fe, Cr, Cu, Zn, Ca,Mg, Zr, S, Si, Na, K and Al, and 1.7≤“f”≤2.1), is added to and stirredin the readied aqueous solution to make a mixed-and-dispersed solution.Subsequently, an acidic metallic-salt aqueous solution is furtheradmixed to and stirred in the above-mentioned mixed-and-dispersedsolution being put in a stirred state. The stirring operation iscontinued for from 15 minutes to one hour approximately. The presentactive material is isolated by filtering.

Treatment 3: an aqueous solution of an ammonium-phosphate salt, or anaqueous solution of a metallic salt and an ammonium-phosphate salt isreadied, and then a material, which belongs to a lamellar rock-salt typeand is expressed by the general formula:Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f) (where 0.2≤“a”≤1, “b”+“c”+“d”+“e”=1,0≤“e”<1, “D” is at least one element selected from the group consistingof Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K and Al, and1.7≤“f”≤2.1), is added at a time to and stirred in the readied aqueoussolution. The stirring operation is continued for from 15 minutes to onehour approximately. The present active material is isolated byfiltering.

Treatment 4: an acidic metallic-salt aqueous solution, and anammonium-phosphate salt aqueous solution are readied, respectively. Amaterial, which belongs to lamellar rock-salt type and is expressed bythe general formula: Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f) (where0.2≤“a”≤1, “b”+“c”+“d”+“e”=1, 0≤“e”<1, “D” is at least one elementselected from the group consisting of Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S,Si, Na, K and Al, and 1.7≤“f”≤2.1), is stirred within ion-exchangedwater to make a mixed-and-dispersed solution. Subsequently, two kinds ofthe aforementioned aqueous solutions are added respectively orsimultaneously to the aforementioned mixed-and-dispersed solution andstirred therein. The present active material is isolated by filtering.

As for the metallic salt used in any of Treatment through Treatment 4, ametallic nitrate having less influences on batteries even when residingin an active material is preferable. As for the metallic nitrate, thefollowing are exemplifiable: magnesium nitrate, barium nitrate,strontium nitrate, aluminum nitrate, or cobalt nitrate.

As for the ammonium-phosphate salt used in any of Treatment 1 throughTreatment 4, the following are exemplifiable: diammonium hydrogenphosphate, ammonium dihydrogen phosphate, or ammonium phosphate. Anespecially preferable option is diammonium hydrogen phosphate. Moreover,as for a method for preparing the ammonium-phosphate salt aqueoussolution, the following are givable: a method of preparing the aqueoussolution by dissolving diammonium hydrogen phosphate, ammoniumdihydrogen phosphate or ammonium phosphate in water; or a method ofpreparing the aqueous solution by mixing a phosphoric acid and ammoniawith each other, and the like. As for the ammonium-phosphate saltaqueous solution used in any of Treatment 1 through Treatment 4, aweakly-alkaline ammonium-phosphate salt aqueous solution is preferable.

The following aqueous solutions used in any of Treatment 1 throughTreatment 4 are not at all limited especially in terms of theconcentrations: the metallic salt aqueous solution, and theammonium-phosphate salt aqueous solution, as well as the aqueoussolutions containing a metallic salt and ammonium-phosphate salt.However, a preferable metallic salt aqueous solution has a metallic saltin a concentration falling within a range of from 0.2 to 10% by mass.Moreover, a preferable ammonium-phosphate salt aqueous solution has anammonium-phosphate salt in a concentration falling within a range offrom 0.2 to 50% by mass. In addition, a preferable aqueous solutioncontains a metallic salt and an ammonium-phosphate salt in aconcentration falling within a range of from 0.2 to 10% by mass,respectively.

Setting up a time for the stirring operation suitably is allowed in anyof Treatment 1 through Treatment 4.

After any of Treatment 1 through Treatment 4, drying and/or calciningthe present active material is also permitted. The drying operation is astep for removing water adhered onto the present active material, iscarried out allowably within a range of from 80 to 150° C. for from oneto 24 hours or from one to 10 hours approximately, and is carriedeffectively even under a depressurized condition. The calciningoperation is a step for fixing the crystallinity of the present activematerial, is carried out permissibly within a range of from 400 to1,200° C., from 500 to 1,100° C. or from 600 to 900° C., for from one to10 hours or from one to 5 hours approximately. After the calcining step,carrying out a pulverization treatment is also allowed to give adesirable particle diameter to the present active material. Note thatthe drying step and/or the calcining step do not have any markedinfluence on the composition ratio in the present active material.However, when the temperature is too low or the time is too short in thecalcining step, such a fear probably arises as the heterogeneous strainsbecome less likely to occur; whereas, when the temperature is too hightherein, such another fear probably arises as atomic rearrangements takeplace so that the heterogeneous strains have disappeared.

The generation of the high manganese portion is ascertainable bymeasuring the surface of an active material after the treatmentaccording to the present invention by an X-ray photoelectronicspectroscopy and then carrying out a composition analysis. A thicknessof the superficial layer including the high manganese portion isascertainable by observing a cut face made by cutting the present activematerial with a transmission electron microscope, or by measuring thecut face with a TEM-EDX, a combination of a transmission electronmicroscope and a dispersion X-ray analyzing device, and then doing acompositional analysis, for instance. Moreover, another compositionratio in any portion other than the superficial layer in the presentactive material is ascertainable by measuring another cut face made bycutting the present active material with a TEM-EDX, a combination of atransmission electron microscope and a dispersion X-ray analyzingdevice, for instance.

Note that, in consideration of the aforementioned specific treatment,the present active material is apparently modified to being Mn rich inthe composition ratio in the active-material superficial layer, althoughno Mn is added thereto by the specific treatment. Hence, a technologyaccording to the present invention is a totally different technologyfrom such a technology as Mn or an Mn-containing compound is added to anactive material to adhere the Mn or Mn -containing compound on or in thevicinity of the active-material surface. Moreover, as being apparentfrom separating an active material from the ammonium phosphate saltaqueous solution by the aforementioned specific treatment, and from thefact that no phosphorous was detected from active materials according toexamples described below, the present active materials and productionprocesses are quite distinct from an active material coated with aphosphorous-containing layer disclosed in Japanese Unexamined PatentPublication (KOKAI) Gazette No. 2003-7299, for instance, and aproduction process for the same disclosed therein.

Although an Mn composition ratio in the superficial layer of the presentactive material becomes high by carrying out the aforementioned specifictreatment, a Co composition therein becomes low contrarily. An Nicomposition ratio also become high in an occasion, or even becomes lowin another occasion. And, in consideration of the Mn composition ratiomodified to be high in the superficial layer of the present activematerial and the Co composition ratio modified to be low thereinregardless of the fact that no Mn is added to the present activematerial by the specific treatment, Co in the superficial layer of amaterial expressed by the general formula:Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f) (where 0.2≤“a”≤1, “b”+“c”+“d”+“e”=1,0≤“e”<1, “D” is at least one element selected from the group consistingof Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K and Al, and 1.7≤“f”≤2.1)is assumably eluted into the aqueous solutions (and Ni therein is alsoeluted thereinto depending on cases) by the aforementioned specifictreatment. As a consequence, changes are assumably enabled to arise inthe superficial-layer composition ratios. The likeliness of eluting intothe aqueous solutions seems to be ordered as follows Co, Ni, and Mn.

If so, the high manganese portion is also expressible by a generalformula: Li_(a3)Ni_(b3)Co_(c3)Mn_(d3)D_(e3)O_(f3) (where 0.2≤“a3”≤1,“b3”+“c3”+“d3”+“e3”<1, 0<“b3”≤“b”, 0<“c3”<“c”, 0<“d3”≤“d”, 0≤“e3”<1, “D”is at least one element selected from the group consisting of Li, Fe,Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K and Al, and 1.7≤“f3”≤2.1).

Moreover, examining the concrete contents of the aforementioned specifictreatment along with the difference between the patterns of integratedstrengths in an image of the first through third superlattice-structureportions according to the present invention observed with a high-anglescattering annular dark-field scanning transmission electron microscopeand the other patterns of integrated strengths in another image of theconventional ordinary superlattice plane obtained therewith, believingas follows is possible in the aforementioned specific treatment: some ofthe metals in the [√3×√3]R30° type ordinary superlattice plane at the 3b sites in the lamellar rock-salt structure have been removeddistinctively. For example, when believing that only Co of the Ni, Coand Mn at the 3 b sites in the lamellar rock-salt structuredLiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ has been removed, the integrated strengthsof the regular first through third superlattice-structure portionsaccording to the present invention are explainable. Understandingbecomes easy probably when supposing an ordinary superlattice plane fromwhich only Co has been removed distinctively in the schematic diagramshown in FIG. 1. That is, the specific treatment is presumed to haveremoved a specific metal distinctively from the superficial layer of amaterial belonging to a lamellar rock-salt type, and expressed by thegeneral formula: Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f) (where 0.2≤a”≤1,“b”+“c”+“d”+“e”=1, 0≤“e”<1, “D” is at least one element selected fromthe group consisting of Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K andAl, and 1.7≤“f”≤2.1). The removal of the specific metal is presumed toresult in strains occurred in the crystals of the aforementionedmaterial. Believing as hereinafter described is also possible: at thecalcining step to be carried out subsequently, interactions betweenhigh-temperature states and stresses arising from the strains in thecrystals to act on the superficial layer lead to generating the firstthrough third superlattice-structure portions with stable crystalstructures.

Constituting the 3 b sites of a [√/3×√3]R30° type in a lamellarrock-salt structure according to the aforementioned general formula isadvantageous.

Hereinafter, relationships between a [√3×√3]R30° type at the 3 b sitesin a lamellar rock-salt structure according to the general formula, andmetallic defects at the 3 b sites resulting from the aforementionedspecific treatment, as well as the first through thirdsuperlattice-structure portions according to the present invention arediscussed. In order to make understanding easy, an instance where the 3b sites are constituted of three elements, Ni, Co and Mn, is supposed.

When the 3 b sites in a lamellar rock-salt structure are constituted ofNi_(1/3)Co_(1/3)Mn_(1/3), the ordinary superlattice plane is expressibleas a [√3×√3]R30° type, as set forth in the above-described literature.When paying attention herein to the valences of which Ni, Co and Mnhave, the metals have stable valences, such as Ni²⁺, Co³⁺ and Mn⁴⁺,respectively, to exist in the 3 b sites. And, the respective metalsadopt a regular [√3×√3]R30° type in compliance with the valences inorder to avoid localizing the positive charges.

Next, another instance where the 3 b sites in a lamellar rock-saltstructure are constituted of Ni_(5/10)Co_(2/10)Mn_(3/10) is examined.Since an average of the valences at the 3 b sites is needed to be “3⁺”,Ni, Co and Mn are not enabled to exist alone as Ni²⁺, Co³⁺ and Mn⁴⁺ withthe stable valences. Since Ni_(5/10)Co_(2/10)Mn_(3/10) is rich in Ni andpoor in Co, compared with Ni_(1/3)Co_(1/3)Mn_(1/3), some of Ni comes toexist as Ni³⁺, instead of deficient Co³⁺. Understanding becomes easyprobably when supposing an ordinary superlattice plane in which Ni hassubstituted for some of Co in the schematic diagram shown in FIG. 1.Hence, even when the 3 b sites in a lamellar rock-salt structure areconstituted of N_(5/10)Co_(2/10)Mn_(3/10), adopting a regular[√3×√3]R30° type in compliance with the valences in order to avoid thelocalizing the positive charges is said to be advantageous for therespective metals.

Likewise, when the 3 b sites in a lamellar rock-salt structure has beenpoor in Ni but becomes rich in Co, compared withNi_(1/3)Co_(1/3)Mn_(1/3), for instance, some of Co comes to exist asCo²⁺, instead of deficient Ni²⁺. Moreover, when the 3 b sites in anotherlamellar rock-salt structure has been poor in Ni but becomes rich in Mn,compared with Ni_(1/3)Co_(1/3)Mn_(1/3), for instance, some of Mn comesto exist as Mn²⁺, instead of deficient Ni²⁺. Therefore, even when thecomposition of the 3 b sites in the lamellar rock-salt structure, whichare constituted of three elements, Ni, Co and Mn, is a composition beingdifferent from Ni_(1/3)Co_(1/3)Mn_(1/3), adopting a regular [√3×√3]R30°type in compliance with the valences in order to avoid localizing thepositive charges is believed to be advantageous for the respectivemetals at the 3 b sites.

And, since the aforementioned specific treatment removes a specificmetal in the 3 b sites selectively, regular metallic defects occur atthe 3 b sites. The first through third superlattice-structure portionsaccording to the present invention are expressions for regular metallicdefects from out of the 3 b sites in an ordinary superlattice plane.Note that, of the three elements (i.e., Ni, Co and Mn), Co is mostlikely to be removed and Mn is least likely to be removed in theaforementioned specific treatment.

In accordance with the above examinations, the superficial layer of amaterial belonging to a lamellar rock-salt type and expressed by thegeneral formula: Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f) (where 0.2≤“a”≤1.2,“b”+“c”+“d”+“e”=1, 0≤“e”<1, “D” is at least one element selected fromthe group consisting of Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K andAl, and 1.7≤“f”≤2.1) to which the aforementioned specific treatment hasbeen carried out is able to generate the first through thirdsuperlattice-structure portions according to the present invention notonly in the instance where the 3 b sites are constituted ofNi_(1/3)Co_(1/3)Mn_(1/3) with “b”=1/3, “c”=1/3, “d”=1/3 and “e”=0 butalso in the other instances.

In accordance with the above mechanism, a preferable surface of aprior-to-specific-treatment material comprises a [√3×√3]R30° typeordinary superlattice plane. However, even when the surface of aprior-to-specific-treatment material does not comprise any ordinarysuperlattice plane, strains in the crystals of the material resultingfrom the aforementioned specific treatment, and stresses concentratingat around the superficial layer of the material, as well as exposing thematerial to high-temperature conditions lead to making rearrangements ofmetallic elements occur in the surface of the material. As a consequent,the following is assumable: the first through thirdsuperlattice-structure portions with stable crystal structures areenabled to arise. Moreover, the occurrence of the following instance isalso assumable: a [√3×√3]R30° type ordinary superlattice plane isenabled to arise in the vicinity of the thus arisen first through thirdsuperlattice-structure portions.

The first through third superlattice-structure portions exist in thesuperficial layer of the present invention active material. Even if themechanism as aforementioned, namely, removing a specific metal, resultsin generating the first through third superlattice-structure portions,the superficial layer accounts for a slightly less volume to the entirevolume of the present active material. Therefore, composition changesoccurred in the first through third superlattice-structure portions donot have any influence virtually on the compositions expressed by thegeneral formula: Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f) (where 0.2≤“a”≤1.2,“b”+“c”+“d”+“e”=1, 0≤“e”<1, “D” is at least one element selected fromthe group consisting of Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K andAl, and 1.7≤“f”≤2.1).

Moreover, the elemental compositions of the high manganese portion andfirst through third superlattice-structure portions were revealed thatthe composition ratios of Mn and oxygen become high. Incidentally, sucha material as Li₂MnO₃ exhibiting a high capacity but being inactive, andan Li₂MnO₃—LiMO₂ solid solution incorporating the material therein(where “M” is a transition metal) have been known recently (for example,see FB Technical News, No. 66, 2011.1, pp. 3-10, Making Lithium-ionBattery Be of High Performance: On Solid-solution Positive-electrodeMaterial by SATO Yuichi). In consideration of the elemental compositionsof the aforementioned high manganese portion and first through thirdsuperlattice-structure portions, there is such a possibility that thehigh manganese portion and first through third superlattice-structureportions partially comprise crystal structures arising in theaforementioned Li₂MnO₃ or Li₂MnO₃—LiMO₂ solid solution, or crystalstructures similar to such structures.

Using the present active material makes a lithium-ion secondary batterymanufacturable. In addition to an electrode (a positive electrode, forinstance) including the present active material, the aforementionedlithium-ion secondary battery further comprises a negative electrode, aseparator and an electrolytic solution, as battery constituent elements.

The positive electrode is constituted of a current collector, and anactive-material layer including the present active material. Note that,in the active-material layer, further including an active material otherthan the present active material is also allowed.

A “current collector” refers to a chemically inactive high electronconductor for keeping an electric current flowing to electrodes duringthe discharging or charging operations of a lithium-ion secondarybattery. As for the current collector, the following are exemplifiable:at least one member selected from the group consisting of silver,copper, gold, aluminum, magnesium, tungsten, cobalt, zinc, nickel, iron,platinum, tin, indium, titanium, ruthenium, tantalum, chromium, andmolybdenum; as well as metallic materials, such as stainless steels.Covering the current collector with a publicly-known protective layer isalso allowed.

The current collector is enabled to have such a form as a foil, a sheet,a film, a linear shape, or a rod-like shape.

Consequently, as the current collector, a metallic foil, such as acopper foil, a nickel foil, an aluminum foil or a stainless-steel foil,is usable suitably. When the current collector has a foiled, sheeted orfilmed form, a preferable thickness thereof falls within a range of from10 μm to 100 μm.

Making the positive electrode is made possible by forming theactive-material layer onto a surface of the current collector.

The active-material layer is permitted to further include a conductiveadditive. The conductive additive is added in order to enhance theelectrically-conducting property of an electrode. As for the conductiveadditive, the following are exemplified: carbonaceous fine particles,such as carbon black, graphite, acetylene black (or AB) and KETJENBLACK(or KB (registered trademark)); and gas-phase-method carbon fibers (orvapor-grown carbon fibers (or VGCF)). One of the conductive additives isaddable independently, or two or more thereof are combinable to add tothe active-material layer. Although an employment amount of theconductive additive is not at all restricted especially, setting theemployment amount is possible, for instance, at from one to 50 parts bymass, or at from one to 30 parts by mass, with respect to the presentactive material in an amount of 100 parts by mass.

The active-material layer is permitted to further include a bindingagent. The binding agent performs a role of fastening the present activematerial and a conductive additive together onto the surface of acurrent collector. As for the binding agent, the following areexemplifiable: fluorine-containing resins, such as polyvinylidenefluoride, polytetrafluoroethylene and fluorinated rubber; thermoplasticresins, such as polypropylene and polyethylene; imide-based resins, suchas polyimide and polyamide-imide; and alkoxysilyl group-containingresins. Although an employment amount of the binding agent is not at allrestricted especially, setting the employment amount is possible at fromfive to 50 parts by mass with respect to the present active material inan amount of 100 parts by mass, for instance.

As for a method of forming an active-material layer onto the surface ofa current collector, the present active material is permitted to becoated onto a surface of the current collector using a heretoforepublicly-known method, such as a roll-coating method, a dip-coatingmethod, a doctor-blade method, a spray-coating method or acurtain-coating method. To be concrete, a composition for forming anactive-material layer including the present active material, as well asa binding agent and conductive additive, if needed, is prepared. Afteradding a proper solvent to the composition to turn the composition intoa paste-like composition, the composition is coated onto a surface ofthe current collector, and is thereafter dried thereon. If needed, thepost-drying composition is also allowed to be compressed in order toenhance the density of an electrode.

As for the solvent, N-methyl-2-pyrrolidone (or NMP), methanol, andmethyl isobutyl ketone (or MIBK) are exemplifiable.

The negative electrode comprises a current collector, and anegative-electrode active-material layer bound together onto a surfaceof the current collector.

The negative-electrode active-material layer includes anegative-electrode active material, as well as a binding agent and/or aconductive additive, if needed.

The current collector, binding agent and conductive additive are thesame as the current collector, binding agent and conductive additiveexplained in the positive electrode.

As for the negative-electrode active material, the following areexemplifiable: carbon-based materials being capable of occluding andreleasing (or sorbing and desorbing) lithium; elements being capable ofalloying with lithium; compounds comprising an element being capable ofalloying with lithium; or polymeric materials.

As for the carbon-based material, the following are exemplifiable:non-graphitizable carbon, artificial graphite, cokes, graphites, glassycarbons, organic-polymer-compound calcined bodies, carbon fibers,activated carbon, or carbon blacks. Note herein that the“organic-polymer-compound calcined bodies” refer to calcined bodiescarbonized by calcining polymeric materials, such as phenols and furans,at a proper temperature.

As for the element being capable of alloying with lithium, the followingare exemplifiable concretely: Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra,Ti, Ag, Zn, Cd, Al, Ga, In, Si, Ge, Sn, Pb, Sb, and Bi. In particular,Si, or Sn is preferred.

As for the compound comprising an element being capable of alloying withlithium, the following are exemplifiable concretely: ZnLiAl, AlSb, SiB₄,SiB₆, Mg₂Si, Mg₂Sn, Ni₂Si, TiSi₂, MoSi₂, CoSi₂, NiSi₂, CaSi₂, CrSi₂,Cu₅Si, FeSi₂, MnSi₂, NbSi₂, TaSi₂, VSi₂, WSi₂, ZnSi₂, SiC, Si₃N₄,Si₂N₂O, SiO_(v) (where 0<“v”≤2), SnO_(w) (where 0<“w”≤2), SnSiO₃, LiSiO,or LiSnO. In particular, SiO_(x) (where 0.3≤“x”≤1.6, or 0.5≤“x”≤1.5) ispreferred.

Among the options, an allowable negative-electrode active materialcomprises an Si-based material including Si. A permissible Si-basedmaterial comprises silicon or/and a silicon compound being capable ofsorbing and desorbing lithium ions. For example, an allowable Si-basedmaterial comprises SiO_(x) (where 0.5≤“x”≤1.5). Although silicon haslarge theoretical charged and discharged capacities, silicon exhibitslarge volumetric changes at the time of charging and dischargingoperations. Hence, making a negative-electrode active material ofSiO_(x) including silicon enables the volumetric changes of silicon tobe relieved.

Moreover, a preferable Si-based material has an Si phase, and an SiO₂phase. The Si phase comprises a silicon elementary substance, is a phasebeing able to sorb and desorb Li ions, and expands and contracts asaccompanied by sorbing and desorbing Li ions. The SiO₂ phase comprisesSiO₂, and makes a buffer phase absorbing the expansions and contractionsof the Si phase. A more preferable Si-based material comprises the Siphase covered by the SiO₂ phase. In addition, an allowable Si-basedmaterial comprises a plurality of the pulverized Si phases integrated toform particles by being covered with the SiO₂ phase. In the instance,the volumetric changes of the entire Si-based material are suppressibleeffectively.

A preferable mass ratio of the SiO₂ phase to the Si phase in theSi-based material is from one to three. When said mass ratio is lessthan one, the expansions and contractions of the Si-based materialbecome large, and so such a fear probably arises that cracks occur inthe negative-electrode active-material layer including the Si-basedmaterial. On the other hand, when said mass ratio exceeds three, theLi-ion sorbing and desorbing amounts of the negative-electrode activematerial become less, and thereby the electric capacitance of a batteryper the negative-electrode unit mass becomes low.

Moreover, as the compound comprising an element capable of undergoing analloying reaction with lithium, tin compounds, such as tin alloys (e.g.,Cu—Sn alloys, Co—Sn alloys, and the like), are exemplifiable.

As for the polymeric material, polyacetylene, and polypyrrole areexemplifiable concretely.

The separator is one of the constituent elements making lithium ionspass therethrough while isolating the positive electrode and negativeelectrode from one another and preventing the two electrodes fromcontacting with each other to result in electric-currentshort-circuiting. As for the separator, the following are exemplifiable,for instance: porous membranes using one member or a plurality ofsynthetic resins, such as polytetrafluoroethylene, polypropylene orpolyethylene; or porous membranes made of ceramics.

The electrolytic solution includes a nonaqueous solvent, and anelectrolyte dissolved in the nonaqueous solvent.

As for the nonaqueous solvent, cyclic esters, linear or chain-shapedesters, ethers, and the like, are employable. As for the cyclic esters,the following are exemplifiable: ethylene carbonate, propylenecarbonate, butylene carbonate, gamma-butyrolactone, vinylene carbonate,2-methyl-gamma-butyrolactone, acetyl-gamma-butyrolactone, andgamma-valerolactone. As for the linear esters, the following areexemplifiable: dimethyl carbonate, diethyl carbonate, dibutyl carbonate,dipropyl carbonate, methyl ethyl carbonate, alkyl propionate ester,dialkyl malonate ester, alkyl acetate ester, and so forth. As for theethers, the following are exemplifiable: tetrahydrofuran,2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane,1,2-diethoxyethane, and 1,2-dibutoxyethane.

As for the electrolyte, a lithium salt, such as LiClO₄, LiAsF₆, LiPF₆,LiBF₄, LiCF₃SO₃ or LiN(CF₃SO₂)₂, is exemplifiable.

As for the electrolytic solution, the following solution isexemplifiable: a solution comprising a lithium salt, such as LiClO₄,LiPF₆, LiBF₄ or LiCF₃SO₃, dissolved in a concentration of from 0.5 mol/Lto 1.7 mol/L approximately in a nonaqueous solvent, such as ethylenecarbonate, dimethyl carbonate, propylene carbonate or diethyl carbonate.

A lithium-ion secondary battery using the present active material isless likely to degrade, and exhibits a suitable capacity maintainedrate, because the lithium-ion secondary battery comprises: the stablehigh manganese portion in the active-material superficial layer; or thestable first through third superlattice-structure portions in theactive-material superficial layer; or a parameter of the heterogeneousstrains in a lamellar rock-salt crystal structure within a suitablerange. As a consequence, the lithium-ion secondary battery using thepresent active material is able to exhibit a satisfactory capacitymaintained rate even under a high-potential driving or operatingcondition. Consequently, the lithium-ion secondary battery using thepresent active material is a battery maintaining large charged anddischarged capacities and having excellent cyclic performance. Noteherein that the “high-potential driving or operating condition” refersto conditions where a lithium-ion operating potential to lithium metalis 4.3 V or more, and is further from 4.4 V to 4.6 V or from 4.5 V to5.5 V. In the lithium-ion secondary battery using the present activematerial, setting a charging potential of the positive electrode ispossible at 4.3 V or more, and further at from 4.4 V to 4.6 V or from4.5 V to 5.5 V, to lithium metal serving as the standard. Note that, inthe driving or operating condition of a common lithium-ion secondarybattery, a lithium-ion operating potential to lithium metal is less than4.3 V.

Since a type of the lithium-ion secondary battery using the presentactive material is not at all limited especially, various types, such ascylindrical types, rectangular types, coin types and laminated types,are adoptable.

The lithium-ion secondary battery using the present active material ismountable in a vehicle. Since the lithium-ion secondary battery usingthe present active material maintains large charged and dischargedcapacities and has excellent cyclic performance, the vehicle having thebattery on-board makes a high-performance vehicle.

As for the vehicle, an allowable vehicle is a vehicle making use ofelectric energies produced by battery for all or some of the powersource. For example, the following are given: electric automobiles,hybrid automobiles, plug-in hybrid automobiles, hybrid railroadvehicles, electric-powered forklifts, electric wheelchairs,electric-power-assisted bicycles, and electric-powered two-wheelvehicles.

Having been described so far are the embodiment modes of the presentactive material for lithium-ion secondary battery. However, the presentinvention is not limited to the aforementioned embodying modes at all.The present invention is feasible in various modes, to which changes ormodifications that one of ordinary skill in the art carries out aremade, within a range not departing from the gist of the presentinvention.

EXAMPLE

Hereinafter, examples and comparative examples are shown, and therebythe present invention is described more concretely. Note that theexamples in the following descriptions do not limit the presentinvention at all. In the following descriptions, the term, “part,” meansa part by mass, and the term, “%,” means a percentage by mass, unlessotherwise specified especially.

First Example

Aforementioned Treatment 1 was followed, thereby carrying out thefollowing treatments to a lithium composite metallic oxide serving as astarting substance.

A lithium composite metallic oxide made by a coprecipitation method andexpressed by LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ was readied. Surface-modifyingaqueous solutions including (NH₄)₂HPO₄in an amount of 4.0% by mass andMg(NO₃)₂ in an amount of 5.8% by mass when each of the aqueous solutionswas taken entirely as 100% by mass wereprepared, respectively. Thelithium composite metallic oxide was immersed into the surface-modifyingaqueous solutions, and was then stirred in the aqueous solutions andmixed therewith at room temperature. The immersion time was set at onehour.

A filtration was carried out after the immersion. Subsequently, thesurface-modified lithium composite metallic oxide was dried at 130° C.for six hours. Thereafter, the obtained lithium composite metallic oxidewas heated at 700° C. under an air atmosphere for five hours. A productobtained by the treatments was labeled an active material according to afirst example.

A lithium-ion secondary battery according to the first example wasfabricated in the following manner.

A positive electrode was made as described below.

An aluminum foil with a thickness of 20 μm was readied to serve as acurrent collector for positive electrode. The following were mixed oneanother: the active material according to the first example in an amountof 94 parts by mass; acetylene black (or AB) serving as a conductiveadditive in an amount of three parts by mass; and polyvinylidenefluoride (or PVdF) serving as a binder in an amount of three parts bymass. The mixture was dispersed in a proper amount ofN-methyl-2-pyrrolidone (or NMP), thereby preparing a slurry. Theaforementioned slurry was put on a surface of the aforementionedaluminum foil, and then the slurry was coated thereon so as to be in theshape of a film using a doctor blade. The NMP was removed by means ofvolatilization by drying the aluminum foil with the slurry coated at 80°C. for 20 minutes, thereby forming an active-material layer on thealuminum-foil surface. The aluminum foil with the active-material layerformed on the surface was compressed using a roll pressing machine,thereby adhesion joining the aluminum foil and the active-material layerfirmly with each other. The joined substance was heated at 120° C. forsix hours with a vacuum drier, and was then cut out to a predeterminedconfiguration (e.g., a rectangular shape with 25 mm×30 mm), therebyobtaining a positive electrode.

A negative electrode was made as described below.

The following were mixed one another: graphite in an amount of 97 partsby mass; KB serving as a conductive additive in an amount of one part bymass; and styrene-butadiene rubber (or SBR) as well as carboxymethylcellulose (or CMC) in an amount of one part by mass, respectively, thetwo serving as a binding agent. The mixture was dispersed in a properamount of ion-exchanged water to prepare a slurry. The slurry was coatedonto a copper foil with a thickness of 20 μm (i.e., a current collectorfor negative electrode) so as to be in the shape of a film using adoctor blade. The copper foil with the slurry coated thereon was dried,and was thereafter pressed. The joined substance was heated at 120° C.,for six hours with a vacuum drier, and was then cut out to apredetermined configuration (e.g., a rectangular shape with 25 mm×30mm), thereby making a negative electrode with a thickness of 85 μmapproximately.

Using the above-mentioned positive electrode and negative electrode, alaminated-type lithium-ion secondary battery was manufactured. To beconcrete, a rectangle-shaped sheet serving as a separator and comprisinga polypropylene/polyethylene/polypropylene three-layered-constructionresinous film with 27×32 mm in size and 25 μm in thickness wasinterposed or held between the positive electrode and the negativeelectrode, thereby making a polar-plate subassembly. After covering thepolar-plate subassembly with laminated films in which two pieces made apair and then sealing the laminated films at the three sides, anelectrolytic solution was injected into the laminated films which hadbeen turned into a bag shape. As for the electrolytic solution, asolution was used: the solution comprised a solvent in which ethylenecarbonate (or EC), and diethyl carbonate (or DEC) had been mixed oneanother in such a ratio as EC:DEC=3:7 by volume; and LiPF₆ dissolved inthe solvent so as to make 1 mol/L. Thereafter, the remaining one sidewas sealed, thereby obtaining a laminated-type lithium-ion secondarybattery in which the four sides were sealed air-tightly and in which thepolar-plate subassembly and electrolytic solution were closedhermetically. Note that the positive electrode and negative electrodewere equipped with a tab connectable electrically with the outside,respectively, and the tabs extended out partially to the outside of thelaminated-type lithium-ion secondary battery.

Via the above steps, the laminated-type lithium-ion secondary batteryaccording to the first example was fabricated.

Second Example

Other than varying the time to 36 hours during which the lithiumcomposite metallic oxide was immersed into the surface-modifying aqueoussolutions, an active material and laminated-type lithium-ion secondarybattery according to a second example were fabricated by the samemethods as described in the first example.

Third Example

Other than varying the respective surface-modifying aqueous solutions toan aqueous solution including (NH₄)₂HPO₄ in an amount of 2.1% by masswhen the entire aqueous solution was taken as 100% by mass and anaqueous solution including Mg(NO₃)₂ in an amount of 3.0% by mass whenthe entire aqueous solution was taken as 100% by mass, respectively, anactive material and laminated-type lithium-ion secondary batteryaccording to a third example were fabricated by the same methods asdescribed in the first example.

Fourth Example

Other than varying the surface-modifying aqueous solutions to an aqueoussolution including (NH₄)₂HPO₄ in an amount of 5.4% by mass when theentire aqueous solution was taken as 100% by mass, an active materialand laminated-type lithium-ion secondary battery according to a fourthexample were fabricated by the same methods as described in the firstexample.

First Comparative Example

Other than using as an active material LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ perse (hereinafter, being sometimes referred to “an untreated productaccording to a first comparative example”), a laminated-type lithium-ionsecondary battery according to a first comparative example wasfabricated by the same method as described in the first example.

First Evaluating Example

Initial capacities of the lithium-ion secondary batteries according tothe first through fourth examples and the first comparative exampleswere measured. A discharged capacity was measured when carrying out a CCdischarging (i.e., constant-current discharging) mode or operation toeach of the batteries to be measured at a rate of 0.33 C with a voltageof 3.0 V after carrying out a CCCV charging (i.e., constant-current andconstant-voltage charging) mode or operation to each of the batteries at25° C.. at a rate of 0.33 C with a voltage of 4.5 V. The thus measureddischarged capacities were labeled the initial capacities.

In addition, each of the batteries to be measured underwent a 4.5-Vcharging/3.0-V discharging cycle for 25 cycles in which a CCCV charging(i.e., constant-current and constant-voltage charging) mode or operationwas carried out to each of the batteries at 55° C.. at a rate of 1 Cwith a voltage of 4.5 V, retaining or leaving each of the batteriesalone for 2.5 hours, and thereafter carrying out a CC discharging (i.e.,constant-current discharging) mode or operation to each of the batteriesat a rate of 0.33 C with a voltage of 3.0 V. Thereafter, dischargedcapacities at a rate of 0.33 C were measured, and then capacitymaintained rates were computed.

The capacity maintained rates (%) were found by the following equation.

Capacity Maintained Rate (%)={(Post-cycle Capacity)/(InitialCapacity)}×100

Note that 1 C refers to a current rate at which a battery is dischargedfor one hour, for instance.

Table 1 shows results of measuring the Ni, Co and Mn composition ratiosin the superficial layer of the active materials, the initialcapacities, the post-25-cycle capacities, and the capacity maintainedrates.

TABLE 1 Capacity Superficial-layer Main- Composition Ratio InitialPost-cycle tained Ni Co Mn Capacity Capacity Rate (b2) (c2) (d2) (mA ·h/g) (mA · h/g) (%) 1st Ex. 0.32 0.21 0.47 172.7 135.6 78.5 2nd Ex. 0.280.10 0.62 157.5 125.0 79.4 3rd Ex. 0.45 0.17 0.38 160.2 116.3 72.6 4thEx. 0.31 0.25 0.44 165.8 100.5 60.6 1st Comp. Ex. 0.33 0.33 0.33 177.385.7 48.3

The Ni, Co and Mn composition ratios in the superficial layer of theactive materials were computed by means of measuring the surface of theactive materials by an X-ray photoelectric spectroscopy. The fact thatthe internal composition ratios of the active materials were not changedwas ascertained by analyzing the internal compositions from a particlecross-sectional direction with a TEM-EDX. Moreover, on the occasion, thedetected signals of Mg and P used in the treatment step were thedetection limits or less of the TEM-EDX analysis at the superficiallayer and interior. That is, in the superficial layer of an activematerial being obtainable at the specific treatment step, an elementadded from the outside is not said to develop the new performance, but amodified surface done by elements included therein from the verybeginning is said to enable the functional improvements to bedemonstrated.

When comparing the respective examples with the comparative example onthe Ni, Co and Mn composition ratios in the superficial layer of theactive materials, the Mn composition was found out to become high evenin any of the examples, whereas the Co composition was found out tobecome low therein on the contrary.

When comparing the first through fourth examples with the firstcomparative example on the capacity maintained rates, the capacitymaintained rates were found out to be upgraded markedly even in any ofthe examples than in the first comparative example.

From the results above, making the Mn composition ratio in thesuperficial layer of an active material higher than the Mn compositionratio of the original (or in the internal) active material is said toresult in turning the active material into an active material exhibitinga favorable capacity maintained rate.

Fifth Example

A lithium composite metallic oxide made by a coprecipitation method andexpressed by LiNi_(5/10)Co_(2/10)Mn_(3/10)O₂ was readied. Except thatthe respective surface-modifying aqueous solutions were hereinaftervaried to an aqueous solution including (NH₄)₂HPO₄ in an amount of 0.4%by mass when the entire aqueous solution was taken as 100% by mass andan aqueous solution including Mg(NO₃)₂ in an amount of 1.4% by mass whenthe entire aqueous solution was taken as 100% by mass, respectively, anactive material according to a fifth example was obtained using the samemethod as described in the first example.

Using the active material obtained as above, a laminated-typelithium-ion secondary battery according to the fifth example wasfabricated by the following method.

Other than using the active material according to the fifth example asan active material, a positive electrode was made in the same manner asthe aforementioned first example.

A negative electrode was made as described below.

The following were mixed one another: carbon-coated SiO_(x) (where0.3≤“x”≤1.6) in an amount of 32 parts by mass; graphite in an amount of50 parts by mass; acetylene black serving as a conductive additive in anamount of eight parts by mass; and polyamide-imide serving as a bindingagent in an amount of 10 parts by mass. The mixture was dispersed in aproper amount of ion-exchanged water to prepare a slurry. The slurry wascoated onto a copper foil with a thickness of 20 μm (i.e., a currentcollector for negative electrode) so as to be in the shape of a filmusing a doctor blade. The current collector with the slurry coatedthereon was dried, and was thereafter pressed. The joined substance washeated at 120° C. for six hours with a vacuum drier, and was then cutout to a predetermined configuration (e.g., a rectangular shape with 25mm×30 mm), thereby making a negative electrode with a thickness of 85 μmapproximately.

Using the above-mentioned positive electrode and negative electrode, alaminated-type lithium-ion secondary battery was manufactured. To beconcrete, a rectangle-shaped sheet serving as a separator and comprisinga polypropylene/polyethylene/polypropylene three-layered-constructionresinous film with 27 X 32 mm in size and 25 μm in thickness wasinterposed or held between the positive electrode and the negativeelectrode, thereby making a polar-plate subassembly. After covering thepolar-plate subassembly with laminated films in which two pieces made apair and then sealing the laminated films at the three sides, anelectrolytic solution was injected into the laminated films which hadbeen turned into a bag shape. As for the electrolytic solution, asolution was used: the solution comprised a solvent in which ethylenecarbonate, methyl ethyl carbonate and diethyl carbonate had been mixedone another in such a ratio as 3:3:4 by volume; and LiPF₆ dissolved inthe solvent so as to make 1 mol/L. Thereafter, the remaining one sidewas sealed, thereby obtaining a laminated-type lithium-ion secondarybattery according to the fifth example in which the four sides weresealed air-tightly and in which the polar-plate subassembly andelectrolytic solution were closed hermetically. Note that the positiveelectrode and negative electrode were equipped with a tab connectableelectrically with the outside, respectively, and the tabs extended outpartially to the outside of the laminated-type lithium-ion secondarybattery.

Sixth Example

Except that the respective surface-modifying aqueous solutions werevaried to an aqueous solution including (NH₄)₂HPO₄ in an amount of 4.0%by mass when the entire aqueous solution was taken as 100% by mass andan aqueous solution including Mg(NO₃)₂ in an amount of 14.0% by masswhen the entire aqueous solution was taken as 100% by mass,respectively, an active material according to a sixth example wasobtained using the same method as described in the fifth example.

Using the active material obtained as above, a laminated-typelithium-ion secondary battery according to the sixth example wasfabricated by the same method as described in the fifth example.

Seventh Example

Except that the respective surface-modifying aqueous solutions werevaried to an aqueous solution including (NH₄)₂HPO₄ in an amount of 0.4%by mass when the entire aqueous solution was taken as 100% by mass andan aqueous solution including Ba(NO₃)₂ in an amount of 1.4% by mass whenthe entire aqueous solution was taken as 100% by mass, respectively, anactive material according to a seventh example was obtained using thesame method as described in the fifth example.

Using the active material obtained as above, a laminated-typelithium-ion secondary battery according to the seventh example wasfabricated by the same method as described in the fifth example.

Eighth Example

Except that the respective surface-modifying aqueous solutions werevaried to an aqueous solution including (NH₄)₂HPO₄ in an amount of 0.9%by mass when the entire aqueous solution was taken as 100% by mass andan aqueous solution including Ba(NO₃)₂ in an amount of 3.5% by mass whenthe entire aqueous solution was taken as 100% by mass, respectively, anactive material according to an eighth example was obtained using thesame method as described in the fifth example.

Using the active material obtained as above, a laminated-typelithium-ion secondary battery according to the eighth example wasfabricated by the same method as described in the fifth example.

Ninth Example

Except that the respective surface-modifying aqueous solutions werevaried to an aqueous solution including (NH₄)₂HPO₄ in an amount of 0.9%by mass when the entire aqueous solution was taken as 100% by mass andan aqueous solution including Sr(NO₃)₂ in an amount of 3.5% by mass whenthe entire aqueous solution was taken as 100% by mass, respectively, anactive material according to a ninth example was obtained using the samemethod as described in the fifth example.

Using the active material obtained as above, a laminated-typelithium-ion secondary battery according to the ninth example wasfabricated by the same method as described in the fifth example.

Tenth Example

Except that the respective surface-modifying aqueous solutions werevaried to an aqueous solution including (NH₄)₂HPO₄ in an amount of 0.2%by mass when the entire aqueous solution was taken as 100% by mass andan aqueous solution including Al(NO₃)₃ in an amount of 0.7% by mass whenthe entire aqueous solution was taken as 100% by mass, respectively, anactive material according to a tenth example was obtained using the samemethod as described in the fifth example.

Using the active material obtained as above, a laminated-typelithium-ion secondary battery according to the tenth example wasfabricated by the same method as described in the fifth example.

Eleventh Example

Except that the respective surface-modifying aqueous solutions werevaried to an aqueous solution including (NH₄)₂HPO₄ in an amount of 0.4%by mass when the entire aqueous solution was taken as 100% by mass andan aqueous solution including Al(NO₃)₃ in an amount of 1.4% by mass whenthe entire aqueous solution was taken as 100% by mass, respectively, anactive material according to an eleventh example was obtained using thesame method as described in the fifth example.

Using the active material obtained as above, a laminated-typelithium-ion secondary battery according to the eleventh example wasfabricated by the same method as described in the fifth example.

Second Comparative Example

Other than using as an active material LiNi_(5/10)CO_(2/10)Mn_(3/10)O₂per se (hereinafter, being sometimes referred to “an untreated productaccording to a second comparative example”), a laminated-typelithium-ion secondary battery according to a second comparative examplewas fabricated by the same method as described in the fifth example.

Second Evaluating Example

Initial capacities of the lithium-ion secondary batteries according tothe fifth through eleventh examples and the second comparative exampleswere measured. A discharged capacity was measured when carrying out a CCdischarging (i.e., constant-current discharging) mode or operation toeach of the batteries to be measured at a rate of 0.33 C with a voltageof 3.0 V after carrying out a CCCV charging (i.e., constant-current andconstant-voltage charging) mode or operation to each of the batteries at25° C., at a rate of 0.33 C with a voltage of 4.5 V. The thus measureddischarged capacities were labeled the initial capacities.

In addition, each of the batteries to be measured underwent acharging/discharging cycle for 200 cycles in which each of the batterieswas charged and discharged at 60° C. at a rate of 1 C with a voltagefalling in a range of from 4.32 V to 3.0 V. Thereafter, dischargedcapacities were measured under the same conditions as described in themeasurement of the initial capacities after leaving each of thebatteries at room temperature for five hours or more. The thus measureddischarged capacities were labeled post-cycle capacities.

The capacity maintained rates (%) were found by the following equation.

Capacity Maintained Rate (%)={(Post-cycle Capacity)/(InitialCapacity)}×100

Table 2 shows results of measuring the Ni, Co and Mn composition ratiosin the superficial layer of the active materials, the initialcapacities, the post-200-cycle capacities, and the capacity maintainedrates.

TABLE 2 Capacity Superficial-layer Main- Composition Ratio InitialPost-cycle tained Ni Co Mn Capacity Capacity Rate (b2) (c2) (d2) (mA ·h/g) (mA · h/g) (%) 5th Ex. 0.45 0.16 0.39 141.9 111.2 78.2 6th Ex. 0.340.11 0.55 112.3 85.9 76.8 7th Ex. 0.46 0.17 0.37 141.6 107.6 76.1 8thEx. 0.43 0.16 0.41 138.3 106.4 76.8 9th Ex. 0.45 0.17 0.39 141.3 108.676.9 10th Ex. 0.47 0.15 0.38 145.2 112.4 77.2 11th Ex. 0.48 0.15 0.38144.0 109.6 76.4 2nd Comp. Ex. 0.50 0.20 0.30 146.9 111.6 76.0

The Ni, Co and Mn composition ratios in the superficial layer of theactive materials were computed by means of measuring the surface of theactive materials by an X-ray photoelectric spectroscopy. Moreover, thefollowing were also ascertained using a TEM-EDX analysis: the internalcomposition ratios of the active materials were not changed; and thedetected signals of Mg, Ba, Sr, Al and P used in the treatment step werethe detection limits or less of the TEM-EDX analysis at the superficiallayer and interior. In the fifth through eleventh examples as well, inthe superficial layer of an active material being obtainable at thespecific treatment step, an element added from the outside is not saidto develop the new performance, but a modified surface done by elementsincluded therein from the very beginning is said to enable thefunctional improvements to be demonstrated.

When comparing the fifth through eleventh examples with the secondcomparative example on the Ni, Co and Mn composition ratios in thesuperficial layer of the active materials, the Mn composition was foundout to become high even in any of the examples, whereas the Cocomposition was found out to become low therein on the contrary. And,when comparing the fifth through eleventh examples with the secondcomparative example on the capacity maintained rates, the capacitymaintained rates were found out to be upgraded more even in any of theexamples than in the comparative example. From the results, making theMn composition ratio in the superficial layer of an active materialhigher than the Mn composition ratio of the original (or in theinternal) active material is said to result in turning the activematerial into an active material exhibiting a favorable capacitymaintained rate.

Note that, in the secondary battery according to the examples, thesecondary batteries (like the seventh example), in which only slightimprovements were observed on the capacity maintained rates, comparedwith the secondary battery according to the second comparative example,at the time after 200 cycles passed, are present. However, incharging/discharging cycles after going beyond 200 cycles, theimprovements on the capacity maintained rates are predicted to expandfurthermore. And, since practical secondary batteries are expected tomaintain satisfiable capacities even in charging/discharging cyclesafter going beyond 200 cycles, even such an extent of thecapacity-maintained-rate improvement observed in the seventh example isa beneficial effect.

The results of testing shown in Table 1 and Table 2 do not at allcontradict with such characteristics of Mn in an active material as “Mnis the most inactive at the time of Li charging/discharging reactions.Although the greater the Mn content is within an active material themore the capacity declines, the greater the Mn content is within anactive material the more the active material excels in the stabilitycontrarily.”

Note herein that, for a lithium composite metallic oxide having alamellar rock-salt structure and expressed by LiNi_(b)Co_(c)Mn_(d)O₂,the following lattice-energy differences are computed using the firstprinciples calculation under the following conditions: initiallattice-energy differences (or “initial−ΔH”) in the respectivecompositions of Ni, Co and Mn; and lattice-energy differences (or“Li-Separation−ΔH”) when 2/3 of lithium has separated from the lithiumcomposite metallic oxide. Table 3 shows the results. Note that a“lattice-energy difference (or −ΔH)” means a difference between anenergy of LiNi_(b)Co_(c)Mn_(d)O₂ with a lamellar rock-salt structure andanother energy when lithium is separated and then each of Ni, Co and Mnis oxidized so that the lamellar rock-salt structure has collapsed.

Software: Quantum Espresso (PWscf)

Exchange-correlation Interaction: GGAPBE Functional

Calculation Method: PAW (i.e., Project Augmented Wave) Method

Wave-function Cut-off: 50Ry

TABLE 3 Entry Ni: “b” Co: “c” Mn: “d” Initial-ΔH Li-separation-ΔH Entry1-1 0.56 0.11 0.33 87.41 51.49 Entry 1-2 0.56 0.17 0.28 86.73 50.82Entry 1-3 0.56 0.22 0.22 86.14 50.25 Entry 2-1 0.50 0 0.50 89.26 53.99Entry 2-2 0.50 0.11 0.39 88.34 52.75 Entry 2-3 0.50 0.17 0.33 87.8852.15 Entry 2-4 0.50 0.22 0.28 87.29 51.60 Entry 2-5 0.50 0.28 0.2286.70 51.03 Entry 3-1 0.44 0.11 0.44 89.21 54.06 Entry 3-2 0.44 0.170.39 88.76 53.46 Entry 3-3 0.44 0.22 0.33 88.33 52.81 Entry 3-4 0.440.28 0.28 87.73 52.25 Entry 3-5 0.44 0.33 0.22 87.24 51.68 Entry 4-10.39 0.22 0.39 89.17 54.12 Entry 4-2 0.39 0.28 0.33 88.75 53.48 Entry4-3 0.39 0.33 0.28 88.26 52.90 Entry 5-1 0.33 0.33 0.33 89.16 54.17Entry 5-2 0.33 0.44 0.22 88.19 53.01

From the results in Entry 1-1 through Entry 1-3, the composition with ahigh Mn ratio is found out to have a larger value of “Li-separation −ΔH”than does the composition with a low Mn ratio when the Ni composition isconstant. The same is find out from the results in Entry 2-1 throughEntry 2-5, Entry 3-1 through Entry 3-5, Entry 4-1 through Entry 4-3, andEntry 5-1 through Entry 5-2. Note herein that, when Ni is constant, alithium composite metallic oxide with a high Mn composition has beenascertained theoretically to be stable in the lithium composite metallicoxide having a lamellar rock-salt structure and expressed byLiNi_(b)Co_(c)Mn_(d)O₂, because the larger the value of “Li-separation−ΔH” is the more stable the lamellar rock-salt structure is.

In consideration of the results of the first principles calculation, theadvantageous effect of improving the capacity maintained rates shown bythe examples according to the present invention owes to the fact that anMn composition becomes high in the superficial layer of the activematerials according to the present invention. That is, the advantageouseffect is said to arise as a consequence of the following: a lamellarrock-salt structure in the active-material superficial layer isstabilized more and accordingly the lamellar rock-salt structure of thepresent active materials is maintained suitably even after undergoingthe cyclic charging/discharging mode or operation.

Therefore, the results shown by the examples are believed to be validnot only for the LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ andLiNi_(5/10)Co_(2/10)Mn_(3/10)O₂ used actually but also for each andevery material expressed by the general formula:Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f) (where 0.2≤“a”≤1, “b”+“c”+“d”+“e”=1,0≤“e”<1, “D” is at least one element selected from the group consistingof Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K and Al, and1.7≤“f”≤2.1).

From the aforementioned results, namely, the present lithium-ionsecondary batteries using the active materials according to the presentinvention exhibited favorable capacity maintained rates, the secondarybatteries were ascertained to excel in the cyclability. Moreover, thepresent active materials were ascertained to be able to maintain thecapacities suitably even under the driving or operating condition atsuch a high potential as 4.3 V or 4.5 V.

Next, a suitable high manganese portion is hereinafter investigated.Table 4 shows the relationships between theprior-to-surface-modification and post-surface-modification Ni, Co andMn compositions based on the results according to the first througheleventh examples. Note that the lower parenthesized lines in thecolumns designated with “Superficial-layer Composition Ratio” showrelationships with the prior-to-surface-modification compositions. Forexample, Ni(“b2”) according to the first example means to multiply 0.33,a prior-to-surface-modification composition, by 0.96.

TABLE 4 Initial Capacity Superficial-layer Composition Ratio CapacityMaintained Rate Ni (“b2) Co (“c2”) Mn (“d2”) (mA · h/g) (%) 1st Ex. 0.320.21 0.47 172.7 78.5 (0.33 × 0.96) (0.33 × 0.63) (0.33 × 1.41) 2nd Ex.0.28 0.10 0.62 157.5 79.4 (0.33 × 0.84) (0.33 × 0.3)  (0.33 × 1.86) 3rdEx. 0.45 0.17 0.38 160.2 72.6 (0.33 × 1.35) (0.33 × 0.51) (0.33 × 1.14)4th Ex. 0.31 0.25 0.44 165.8 60.6 (0.33 × 0.93) (0.33 × 0.75) (0.33 ×1.32) 1st Comp. Ex. 0.33 0.33 0.33 177.3 48.3 5th Ex. 0.45 0.16 0.39141.9 78.2 (0.5 × 0.9) (0.2 × 0.8) (0.3 × 1.3) 6th Ex. 0.34 0.11 0.55112.3 76.8  (0.5 × 0.68)  (0.2 × 0.55) (0.3 × 1.8) 7th Ex. 0.46 0.170.37 141.6 76.1  (0.5 × 0.92)  (0.2 × 0.85)  (0.3 × 1.23) 8th Ex. 0.430.16 0.41 138.3 76.8  (0.5 × 0.86) (0.2 × 0.8)  (0.3 × 1.37) 9th Ex.0.45 0.17 0.39 141.3 76.9 (0.5 × 0.9)  (0.2 × 0.85) (0.3 × 1.3) 10th Ex.0.47 0.15 0.38 145.2 77.2  (0.5 × 0.94)  (0.2 × 0.75)  (0.3 × 1.27) 11thEx. 0.48 0.15 0.38 144.0 76.4  (0.5 × 0.96)  (0.2 × 0.75)  (0.3 × 1.27)2nd Comp. Ex. 0.5  0.2  0.3  146.9 76.0 Theprior-to-surface-modification compositions of Ni, Co, and Mn are labeled“b,” “c,” and “d,” respectively.

In Table 4, “b2” falls within a range of 0.68×“b”≤“b2”≤1.35×“b”. Hence,“b2” making both of the initial capacity and capacity maintained ratesuitable is presumed to fall within a range of 0.88×“b”<“b2”≤0.96×“b”.

In Table 4, “c2” falls within a range of 0.3×“c”≤“c2”≤0.85×“c”. Hence,“c2” making both of the initial capacity and capacity maintained ratesuitable is presumed to fall within a range of 0.63×“c”≤“c2”≤0.85×“c”.

In Table 4, “d2” falls within a range of 1.14×“d”≤“d2”≤1.86×“d”. Hence,“d2” making both of the initial capacity and capacity maintained ratesuitable is presumed to fall within a range of 1.2×“d”<“d2”≤1.41×“d”.

Third Evaluating Example

The particles of the active material according to the first example andthe particles of the untreated product according to the firstcomparative example were provided with a cross section, respectively, byan Ar-ion milling method using an ion slicer (e.g., “EM-09100IS,” aproduct of NIHON DENSHI Co., Ltd.), and then an analysis on the crosssections was executed by a TEM-EDX. Table 5 lists results of theanalysis at sites of which the distance from the active-materialsuperficial layer was 5 nm and 20 nm. Note that the values of Ni, Co andMn in Table 5 are percentages of the respective metals with respect tothe summed amounts of Ni, Co and Mn. Moreover, the values of O thereinare percentages of O with respect to the summed amounts of Ni, Co, Mnand O.

TABLE 5 5 nm 20 nm 1st Ex. Ni 32.66% 31.74% Co 24.32% 35.18% Mn 43.02%33.08% O 62.44% 51.92% Untreated Ni 34.14% 34.50% Product Co 33.64%34.23% Mn 33.22% 31.27% O 49.71% 49.59%

The present active material was confirmed to have a low Co ratio but ahigh Mn ratio in the vicinity of the superficial layer. Moreover, thesuperficial-layer-vicinity oxygen ratio was confirmed to be high.

Fourth Evaluating Example

Using a high-angle scattering annular dark-field scanning transmissionelectron microscope (e.g., “JEM-ARM200F” produced by NIHON DENSHI Co.,Ltd. (or JEOL)), the superficial layer of the active material accordingto the first example was measured with an acceleration voltage of 200 kVwhile carrying out the spherical aberration correction.

FIG. 2 shows an image obtained by observing the 3 b sites in thelamellar rock-salt structure of the active material from a <1-100>orientation by means of a high-angle scattering annular dark-fieldscanning transmission electron spectroscopy, the image corresponding tothe first through third superlattice-structure portions according to thepresent invention. The long side of a rectangular parallelepiped presenton the lower left in FIG. 2 has a length of 1 nm.

For comparison, FIG. 3 shows an image of an ordinary superlattice planeobtained by observing the 3 b sites in the lamellar rock-salt structureof commercial available LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ per se from a<1-100> orientation. The long side of a rectangular parallelepipedpresent on the lower left in FIG. 3 has a length of 1 nm.

When comparing the images in FIG. 2 and FIG. 3 with each another, imageswith comparable strengths are observed regularly in FIG. 3, whereasimages with “light, light and dark” strengths making a set were observedperiodically.

FIG. 4 shows an image of the interface between a phase comprising thecrystal construction including the first through thirdsuperlattice-structure portions according to the present invention andanother phase comprising a crystal structure including an ordinarysuperlattice plane, the image obtained by observing the 3 b sites in thelamellar rock-salt structure of the present active material from a<1-100> orientation.

FIG. 5 shows data on integrated strengths of the 3 b-site images labeledNos. 1 through No. 7 in FIG. 4. Note that Nos. 1 through 7 in FIG. 4 andFIG. 5 are labels designated for convenience. For example, No. 1 is notat all a label meaning the outermost surface of the present activematerial.

The numerical values in FIG. 5 is hereinafter described. “1004416” inthe line labeled No. 1 is an integrated strength appeared at a site “a”labeled for convenience. The numerical values mean integrated strengthsbeing continuous in the order of from “a” to “b,” “c,”and soon. Thenumerical values set forth in the columns under the integrated strengthsare strength ratios. For example, “0.822” set forth in the column underthe integrated strength of “c” is a strength ratio obtained by dividinga minimum value of the three continuous integrated strengths of “a,” “b”and “c” by a maximum value thereof. “0.813” set forth in the columnunder the integrated strength of “d” is a strength ratio obtained bydividing a minimum value of the three continuous integrated strengths of“b,” “c” and “d” by a maximum value thereof. The respective averagedvalues “n” in the most right column in the table are averaged values ofthe respective seven sets in which the aforementioned strength ratiosmake seven constituent members.

In FIG. 5, Nos. 1 through 4 of which the averaged values “n” satisfysuch a condition as being less than 0.9 make the firstsuperlattice-structure portion according to the present invention.

Moreover, in FIG. 5, “a,” “b” and “c” in the line labeled No. 1, “b,”“c” and “d” in the line labeled No. 2, “d,” “e” and “f” in the linelabeled No. 3, and “c,” “d” and “e” in the line labeled No. 4, forinstance, satisfy the condition on the second superlattice-structureportion according to the present invention.

Hence, the active material according to the first example comprised thefirst through third superlattice-structure portions according to thepresent invention as shown in the lines labeled Nos. 1 through 4 in FIG.5.

Twelfth Example

Aforementioned Treatment 1 was followed, thereby carrying out thefollowing treatments to a lithium composite metallic oxide serving as astarting substance.

A lithium composite metallic oxide made by a coprecipitation method andexpressed by LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ was readied. Surface-modifyingaqueous solutions including (NH₄)₂HPO₄in an amount of 4.0% by mass andMg(NO₃)₂ in an amount of 5.8% by mass when each of the aqueous solutionswas taken entirely as 100% mass were prepared, respectively. The lithiumcomposite metallic oxide was immersed into the surface-modifying aqueoussolutions, and was then stirred in the aqueous solutions and mixedtherewith at room temperature. The immersion time was set at 30 minutes.

A filtration was carried out after the immersion. Subsequently, thesurface-modified lithium composite metallic oxide was dried at 130° C.for six hours. Thereafter, the obtained lithium composite metallic oxidewas heated at 700° C. under an air atmosphere for five hours. A productobtained by the treatments was labeled an active material according to atwelfth example.

A lithium-ion secondary battery according to the twelfth example wasfabricated in the following manner.

A positive electrode was made as described below.

An aluminum foil with a thickness of 20 μm was readied to serve as acurrent collector for positive electrode. The following were mixed oneanother: the active material according to the twelfth example in anamount of 94 parts by mass; acetylene black (or AB) serving as aconductive additive in an amount of three parts by mass; andpolyvinylidene fluoride (or PVdF) serving as a binder in an amount ofthree parts by mass. The mixture was dispersed in a proper amount ofN-methyl-2-pyrrolidone (or NMP), thereby preparing a slurry. Theaforementioned slurry was put on a surface of the aforementionedaluminum foil, and then the slurry was coated thereon so as to be in theshape of a film using a doctor blade. The NMP was removed by means ofvolatilization by drying the aluminum foil with the slurry coated at 80°C. for 20 minutes, thereby forming an active-material layer on thealuminum-foil surface. The aluminum foil with the active-material layerformed on the surface was compressed using a roll pressing machine,thereby adhesion joining the aluminum foil and the active-material layerfirmly with each other. The joined substance was heated at 120° C. for12 hours or more with a vacuum drier, and was then cut out to apredetermined configuration (e.g., a circular shape with 14 mm indiameter), thereby obtaining a positive electrode.

A negative electrode was made as described below.

The following were mixed one another: graphite in an amount of 97 partsby mass; KB serving as a conductive additive in an amount of one part bymass; and styrene-butadiene rubber (or SBR) as well as carboxymethylcellulose (or CMC) in an amount of 20/17 part by mass and 14/17 parts bymass, respectively, the two serving as a binding agent. The mixture wasdispersed in a proper amount of ion-exchanged water to prepare a slurry.The slurry was coated onto a copper foil with a thickness of 20 μm(i.e., a current collector for negative electrode) so as to be in theshape of a film using a doctor blade. The copper foil with the slurrycoated thereon was dried, and was thereafter pressed. The joinedsubstance was heated at 200° C. for two hours with a vacuum drier, andwas then cut out to a predetermined configuration (e.g., a circularshape with 14 mm in diameter), thereby making a negative electrode.

Using the above-mentioned positive electrode and negative electrode, acoin-type lithium-ion secondary battery was manufactured. To beconcrete, a rectangle-shaped sheet serving as a separator and comprisinga polypropylene/polyethylene/polypropylene three-layered-constructionresinous film was interposed or held between the positive electrode andthe negative electrode, thereby making a polar-plate subassembly. Afterputting the polar-plate subassembly in a coin-type case and theninjecting an electrolytic solution into the coin-type case, thecoin-type case was closed hermetically. As for the electrolyticsolution, a solution was used: the solution comprised a solvent in whichethylene carbonate (or EC), and diethyl carbonate (or DEC) had beenmixed one another in such a ratio as EC:DEC=3:7 by volume; and LiPF₆dissolved in the solvent so as to make 1 mol/L.

Via the above steps, the coin-type lithium-ion secondary batteryaccording to the twelfth example was fabricated.

Thirteenth Example

Aforementioned Treatment 2 was followed, thereby carrying out thefollowing treatments to a lithium composite metallic oxide serving as astarting substance.

A lithium composite metallic oxide made by a coprecipitation method andexpressed by LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ was readied. Asurface-modifying aqueous solution including (NH₄)₂HPO₄ in an amount of37% by mass was prepared. The lithium composite metallic oxide wasimmersed into the surface-modifying aqueous solution, and was thenstirred in the aqueous solution and mixed therewith at room temperature.The immersion time was set at 30 minutes.

A filtration was carried out after the immersion. Subsequently, thesurface-modified lithium composite metallic oxide was dried at 130° C.for six hours. Thereafter, the obtained lithium composite metallic oxidewas heated at 700° C. under an air atmosphere for five hours. A productobtained by the treatments was labeled an active material according to athirteenth example.

Other than employing the active material according to the thirteenthexample as an active material, a coin-type lithium-ion secondary batteryaccording to the thirteenth example was hereinafter fabricated by thesame production method as described in the twelfth example.

Third Comparative Example

Other than using LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ per se (e.g., acommercially available product (hereinafter, being sometimes referred to“an untreated product according to a third comparative example”)) for anactive material, a coin-type lithium-ion secondary battery according toa third comparative example was fabricated by the same method asdescribed in the twelfth example. Note that the treatment according tothe present invention was not done to the commercially available productat all.

Fourth Comparative Example

Other than employing an aqueous solution including (NH₄)₂HPO₄ in anamount of 5.4% by mass as a surface-modifying aqueous solution, anactive material and coin-type lithium-ion secondary battery according toa fourth comparative example were fabricated by the same productionmethod as described in the thirteenth example.

Fifth Evaluating Example

The active materials according to the fifth, seventh, ninth, tenth,twelfth and thirteenth examples, the untreated products according to thesecond and third comparative examples, and the active material accordingto the fourth comparative example were measured for X-ray diffractionpatterns by an X-ray diffraction apparatus (e.g., “SmartLab” produced byRIGAKU Corporation). FIG. 7 shows the X-ray diffraction patterns of theactive material according to the twelfth example and untreated productaccording to the third comparative example. In FIG. 7, the solid line isthe diffraction pattern of the active material according to the twelfthexample, and the dotted line is the diffraction pattern of the untreatedproduct according to the third comparative example. From among therespective diffraction patterns, peaks of the (006), (009) and (0012)crystal planes derived from the lamellar rock-salt crystal structure ofthe lithium composite metallic oxide were detected. Usingabove-mentioned Equation (4), c-axis-direction heterogeneous strainsη_(c) were computed from integrated widths β of the three peaks.Moreover, all-round-direction heterogeneous strains η were computed fromintegrated widths β of all peaks derived from the lamellar rock-saltcrystal structure of the lithium composite metallic oxide, the peaksdetected in the measurement field where 2θ was from 5 degrees up to 90degrees. Table 6 shows the materials before the treatments according tothe present invention, the c-axis-direction heterogeneous strains C theall-round-direction heterogeneous strains η, and the ratios η_(c)/η,regarding the respective active materials.

TABLE 6 Prior-to-Present-Treatment Product*) η_(c) η η_(c)/η 5th Ex.Ni_(5/10)Co_(2/10)Mn_(3/10) 0.05 0.09 0.56 7th Ex.Ni_(5/10)Co_(2/10)Mn_(3/10) 0.05 0.08 0.63 9th Ex.Ni_(5/10)Co_(2/10)Mn_(3/10) 0.04 0.08 0.50 10th Ex.Ni_(5/10)Co_(2/10)Mn_(3/10) 0.04 0.09 0.44 2nd Comp.Ni_(5/10)Co_(2/10)Mn_(3/10) 0.08 0.09 0.89 Ex. 12th Ex.Ni_(1/3)Co_(1/3)Mn_(1/3) 0.059 0.063 0.94 13th Ex.Ni_(1/3)Co_(1/3)Mn_(1/3) 0.075 0.087 0.86 3rd Comp.Ni_(1/3)Co_(1/3)Mn_(1/3) 0.033 0.040 0.83 Ex. 4th Comp.Ni_(1/3)Co_(1/3)Mn_(1/3) 0.040 0.059 0.68 Ex. *)Note that“Ni_(5/10)Co_(2/10)Mn_(3/10)” addresses the instance where theprior-to-present-treatment material was LiNi_(5/10)Co_(2/10)Mn_(3/10)O₂.Moreover, “Ni_(1/3)Co_(1/3)Mn_(1/3)” addresses the instance where theprior-to-present-treatment material was LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂. Inaddition, the lines labeled “2nd Comp. Ex. and 3rd Comp. Ex.” addressthe materials used for reference, although no treatment according to thepresent invention was carried out to the comparative examples.

When the material undergone the treatment according to the presentinvention was LiNi_(5/10)Co_(2/10)Mn_(3/10)O₂, the treatment accordingto the present invention was found out to make the values of η_(c) andη_(c)/η small. On the other hand, when the material undergone thetreatment according to the present invention wasLiNi_(1/3)Co_(1/3)Mn_(1/3)O₂, the treatment according to the presentinvention was found out to make the c-axis-direction heterogeneousstrains η_(c) and all-round-direction heterogeneous strains η large, andthereby the values of η_(c)/η changed.

Sixth Evaluating Example

To the active material according to the twelfth example and untreatedproduct according to the third comparative example, a compositionanalysis was carried out by an SEM-EDX method. FIG. 8 shows a chart onresults of the analyses. The compositions of both of the active materialaccording to the twelfth example and untreated product according to thethird comparative example were the same with each virtually. However, inthe active material according to the twelfth example, peaks derived fromimpurities such as S, Al and Zr were hardly observed, the peaks observedin the untreated product according to the third comparative example.

Seventh Evaluating Example

The lithium-ion secondary batteries according to the twelfth andthirteenth examples, and the lithium-ion secondary batteries accordingto the third and fourth comparative examples were evaluated by the samemethod as described in the first evaluating example. However, thecharging/discharging cycle was set to be done 50 cycles.

Table 7 shows the results.

TABLE 7 Initial Post-cycle Capacity Capacity Capacity Maintained Rate(mA · h/g) (mA · h/g) (%) 12th Ex. 165 136 82% 13th Ex. 160 105 66% 3rdComp. Ex. 168 78 46% 4th Comp. Ex. 172 72 42%

Taking the results shown in Table 6 and Table 7 into considerationaltogether, the treatment according to the present invention was foundout to make the η_(c) and η values of the active material large, andthereby the capacity maintained rates of the lithium-ion secondarybatteries comprising the active material changed, when the materialundergone the treatment according to the present invention wasLiNi_(1/3)Co_(1/3)Mn_(1/3)O₂. And, the capacity maintained rate of alithium-ion secondary battery comprising an active material was found tobecome remarkably excellent, when the η_(c)/η value of the activematerial became 0.86 or more.

Moreover, Table 8 below shows the results shown in FIG. 6 along with theresults shown in Table 2, regarding the lithium-ion secondary batteriesaccording to the fifth, seventh, ninth and tenth examples as well as thesecond comparative example. From the results shown in Table 8, thetreatment according to the present invention was found out to make theη_(c)/η values of the active material small, and thereby the capacitymaintained rates of the lithium-ion secondary batteries comprising theactive material changed, when the material undergone the treatmentaccording to the present invention was LiNi_(5/10)Co_(2/10)Mn_(3/10)O₂.And, the capacity maintained rate of a lithium-ion secondary batterycomprising an active material was found to become excellent, when theη_(c)/η value of the active material falls in a range of from 0.44 to0.69.

TABLE 8 Initial Post-cycle Capacity Capacity Capacity Maintained η_(c) ηη_(c)/η (mA · h/g) (m · Ah/g) Rate (%) 5th Ex. 0.05 0.09 0.56 141.9111.2 78.2 7th Ex. 0.05 0.08 0.63 141.6 107.6 76.1 9th Ex. 0.04 0.080.50 141.3 108.6 76.9 10th Ex. 0.04 0.09 0.44 145.2 112.4 77.2 2nd Comp.0.08 0.09 0.89 146.9 111.6 76.0 Ex.

Moreover, in the aforementioned first and twelfth examples, the time forimmersing the lithium composite metallic oxide into thesurface-modifying aqueous solutions was 30 minutes and one hour,respectively. Note herein that no great battery-performance differenceresulting from the immersing-time difference was ascertained because anyof the secondary batteries according to the first and twelfth exampleshad the remarkably excellent capacity maintained rates (see Table 1 andTable 7).

In addition, in the aforementioned first and twelfth examples, the typesof the secondary batteries were a laminated type and a coin type,respectively. Note herein that no great battery-performance differenceresulting from the secondary-battery-type difference was ascertainedbecause any of the secondary batteries according to the first andtwelfth examples had the remarkably excellent capacity maintained ratesas described above. That is, regardless of categories of the types, suchas cylindrical types, rectangular types, coin types and laminated types,a lithium-ion secondary battery using the present active materialexhibits an excellent capacity maintained rate.

Note that, in the present description, the secondary-battery evaluationswere executed to three samples (namely, “n”=3) for the respectivesecondary batteries. And, the initial capacities and post-cyclecapacities set forth in the respective tables were averaged values foreach “n”=3. Moreover, various factors, such as differences betweenraw-material lots and testing dates, have been well known commonly tocause fluctuations in the initial capacity and post-cycle capacity, aswell as in the capacity maintained rate. For example, in the presentevaluating examples, the potential occurrence of fluctuations from 10 to15 mA·h/g approximately in the initial capacity and post-cycle capacityhas been ascertained already even when the retests are carried out underthe identical testing conditions. Although the fluctuations influencefluctuations in the capacity maintained rate as well, saying is possiblethat the benefits that the present invention effects are universalbenefits to various outer disturbance factors, because the benefits ofimprovements resulting from the present invention and the tendenciesthereof do not change at all.

1. An active material having a lamellar rock-salt structure, andexpressed by a general formula, Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f)(where 0.2≤“a”≤1, “b”+“c”+“d”+“e”=1, 0≤“e”<1, “D” is at least oneelement selected from the group consisting of Li, Fe, Cr, Cu, Zn, Ca,Mg, Zr, S, Si, Na, K and Al, and 1.7≤“f”≤2.1); and the active materialcomprising a first superlattice-structure portion in an active-materialsuperficial layer thereof, the first superlattice-structure portionexhibiting a seven-set averaged value “n” of intensity ratios being lessthan 0.9 when the intensity ratios are computed in seven sets bydividing a minimum value of three continuous integrated intensities ofan image, which is obtained by observing identical 3 b sites in saidlamellar rock-salt structure from a <1-100> orientation with ahigh-angle scattering annular dark-field scanning transmission electronmicroscope, by a maximum value of the three continuous integratedintensities.
 2. An active material having a lamellar rock-saltstructure, and expressed by a general formula,Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f) (where 0.2≤“a”≤1, “b”+“c”+“d”+“e”=1,0≤“e”<1, “D” is at least one element selected from the group consistingof Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K and Al, and1.7≤“f”≤2.1); and the active material comprising a secondsuperlattice-structure portion in an active-material superficial layerthereof, wherein three arbitrary continuous integrated strengths of animage, which is obtained by observing identical 3 b sites in saidlamellar rock-salt structure from a <1-100> orientation with ahigh-angle scattering annular dark-field scanning transmission electronmicroscope, are expressed in the following order: p1, p2, and q (where0.9×“p1”≤“p2”≤1.1×“p1”, “q” is “q”<0.9×“p2” when “p1”≤“p2”, or “q” is“q”<0.9×“p1” when “p2”≤“p1”).
 3. An active material having a lamellarrock-salt structure, and expressed by a general formula,Li_(a)Ni_(b)Co_(c)Mn_(d)D_(e)O_(f) (where 0.2≤“a”≤1, “b”+“c”+“d”+“e”=1,0≤“e”<1, “D” is at least one element selected from the group consistingof Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K and Al, and1.7≤“f”≤2.1); and the active material comprising a thirdsuperlattice-structure portion in an active-material superficial layerthereof, the third superlattice-structure portion satisfying theconditions for the first superlattice-structure portion as set forth inclaim 10 and the conditions for a second superlattice-structure portionincluding three arbitrary continuous integrated strengths of an image,which is obtained by observing identical 3 b sites in said lamellarrock-salt structure from a <1-100> orientation with a high-anglescattering annular dark-field scanning transmission electron microscope,are expressed in the following order: p1, p2, and q (where0.9×“p1”≤“p2”≤1.1×“p1”, “q” is “q”<0.9×“p2” when “p1”≤“p2”, or “q” is“q”<0.9×“p1” when “p2”≤“p1”).